Java tutorial
/* * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; import java.io.IOException; import java.io.ObjectOutputStream; import java.io.Serializable; import java.lang.reflect.Array; import java.util.function.BiConsumer; import java.util.function.BiFunction; import java.util.function.Consumer; import java.util.function.Function; import java.util.function.IntFunction; import java.util.function.Predicate; import java.util.function.UnaryOperator; import java.util.stream.IntStream; import java.util.stream.Stream; import java.util.stream.StreamSupport; /** * This class consists exclusively of static methods that operate on or return * collections. It contains polymorphic algorithms that operate on * collections, "wrappers", which return a new collection backed by a * specified collection, and a few other odds and ends. * * <p>The methods of this class all throw a {@code NullPointerException} * if the collections or class objects provided to them are null. * * <p>The documentation for the polymorphic algorithms contained in this class * generally includes a brief description of the <i>implementation</i>. Such * descriptions should be regarded as <i>implementation notes</i>, rather than * parts of the <i>specification</i>. Implementors should feel free to * substitute other algorithms, so long as the specification itself is adhered * to. (For example, the algorithm used by {@code sort} does not have to be * a mergesort, but it does have to be <i>stable</i>.) * * <p>The "destructive" algorithms contained in this class, that is, the * algorithms that modify the collection on which they operate, are specified * to throw {@code UnsupportedOperationException} if the collection does not * support the appropriate mutation primitive(s), such as the {@code set} * method. These algorithms may, but are not required to, throw this * exception if an invocation would have no effect on the collection. For * example, invoking the {@code sort} method on an unmodifiable list that is * already sorted may or may not throw {@code UnsupportedOperationException}. * * <p>This class is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @author Josh Bloch * @author Neal Gafter * @see Collection * @see Set * @see List * @see Map * @since 1.2 */ public class Collections { // Suppresses default constructor, ensuring non-instantiability. private Collections() { } // Algorithms /* * Tuning parameters for algorithms - Many of the List algorithms have * two implementations, one of which is appropriate for RandomAccess * lists, the other for "sequential." Often, the random access variant * yields better performance on small sequential access lists. The * tuning parameters below determine the cutoff point for what constitutes * a "small" sequential access list for each algorithm. The values below * were empirically determined to work well for LinkedList. Hopefully * they should be reasonable for other sequential access List * implementations. Those doing performance work on this code would * do well to validate the values of these parameters from time to time. * (The first word of each tuning parameter name is the algorithm to which * it applies.) */ private static final int BINARYSEARCH_THRESHOLD = 5000; private static final int REVERSE_THRESHOLD = 18; private static final int SHUFFLE_THRESHOLD = 5; private static final int FILL_THRESHOLD = 25; private static final int ROTATE_THRESHOLD = 100; private static final int COPY_THRESHOLD = 10; private static final int REPLACEALL_THRESHOLD = 11; private static final int INDEXOFSUBLIST_THRESHOLD = 35; /** * Sorts the specified list into ascending order, according to the * {@linkplain Comparable natural ordering} of its elements. * All elements in the list must implement the {@link Comparable} * interface. Furthermore, all elements in the list must be * <i>mutually comparable</i> (that is, {@code e1.compareTo(e2)} * must not throw a {@code ClassCastException} for any elements * {@code e1} and {@code e2} in the list). * * <p>This sort is guaranteed to be <i>stable</i>: equal elements will * not be reordered as a result of the sort. * * <p>The specified list must be modifiable, but need not be resizable. * * @implNote * This implementation defers to the {@link List#sort(Comparator)} * method using the specified list and a {@code null} comparator. * * @param <T> the class of the objects in the list * @param list the list to be sorted. * @throws ClassCastException if the list contains elements that are not * <i>mutually comparable</i> (for example, strings and integers). * @throws UnsupportedOperationException if the specified list's * list-iterator does not support the {@code set} operation. * @throws IllegalArgumentException (optional) if the implementation * detects that the natural ordering of the list elements is * found to violate the {@link Comparable} contract * @see List#sort(Comparator) */ @SuppressWarnings("unchecked") public static <T extends Comparable<? super T>> void sort(List<T> list) { list.sort(null); } /** * Sorts the specified list according to the order induced by the * specified comparator. All elements in the list must be <i>mutually * comparable</i> using the specified comparator (that is, * {@code c.compare(e1, e2)} must not throw a {@code ClassCastException} * for any elements {@code e1} and {@code e2} in the list). * * <p>This sort is guaranteed to be <i>stable</i>: equal elements will * not be reordered as a result of the sort. * * <p>The specified list must be modifiable, but need not be resizable. * * @implNote * This implementation defers to the {@link List#sort(Comparator)} * method using the specified list and comparator. * * @param <T> the class of the objects in the list * @param list the list to be sorted. * @param c the comparator to determine the order of the list. A * {@code null} value indicates that the elements' <i>natural * ordering</i> should be used. * @throws ClassCastException if the list contains elements that are not * <i>mutually comparable</i> using the specified comparator. * @throws UnsupportedOperationException if the specified list's * list-iterator does not support the {@code set} operation. * @throws IllegalArgumentException (optional) if the comparator is * found to violate the {@link Comparator} contract * @see List#sort(Comparator) */ @SuppressWarnings({ "unchecked", "rawtypes" }) public static <T> void sort(List<T> list, Comparator<? super T> c) { list.sort(c); } /** * Searches the specified list for the specified object using the binary * search algorithm. The list must be sorted into ascending order * according to the {@linkplain Comparable natural ordering} of its * elements (as by the {@link #sort(List)} method) prior to making this * call. If it is not sorted, the results are undefined. If the list * contains multiple elements equal to the specified object, there is no * guarantee which one will be found. * * <p>This method runs in log(n) time for a "random access" list (which * provides near-constant-time positional access). If the specified list * does not implement the {@link RandomAccess} interface and is large, * this method will do an iterator-based binary search that performs * O(n) link traversals and O(log n) element comparisons. * * @param <T> the class of the objects in the list * @param list the list to be searched. * @param key the key to be searched for. * @return the index of the search key, if it is contained in the list; * otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The * <i>insertion point</i> is defined as the point at which the * key would be inserted into the list: the index of the first * element greater than the key, or {@code list.size()} if all * elements in the list are less than the specified key. Note * that this guarantees that the return value will be >= 0 if * and only if the key is found. * @throws ClassCastException if the list contains elements that are not * <i>mutually comparable</i> (for example, strings and * integers), or the search key is not mutually comparable * with the elements of the list. */ public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) { if (list instanceof RandomAccess || list.size() < BINARYSEARCH_THRESHOLD) return Collections.indexedBinarySearch(list, key); else return Collections.iteratorBinarySearch(list, key); } private static <T> int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key) { int low = 0; int high = list.size() - 1; while (low <= high) { int mid = (low + high) >>> 1; Comparable<? super T> midVal = list.get(mid); int cmp = midVal.compareTo(key); if (cmp < 0) low = mid + 1; else if (cmp > 0) high = mid - 1; else return mid; // key found } return -(low + 1); // key not found } private static <T> int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key) { int low = 0; int high = list.size() - 1; ListIterator<? extends Comparable<? super T>> i = list.listIterator(); while (low <= high) { int mid = (low + high) >>> 1; Comparable<? super T> midVal = get(i, mid); int cmp = midVal.compareTo(key); if (cmp < 0) low = mid + 1; else if (cmp > 0) high = mid - 1; else return mid; // key found } return -(low + 1); // key not found } /** * Gets the ith element from the given list by repositioning the specified * list listIterator. */ private static <T> T get(ListIterator<? extends T> i, int index) { T obj = null; int pos = i.nextIndex(); if (pos <= index) { do { obj = i.next(); } while (pos++ < index); } else { do { obj = i.previous(); } while (--pos > index); } return obj; } /** * Searches the specified list for the specified object using the binary * search algorithm. The list must be sorted into ascending order * according to the specified comparator (as by the * {@link #sort(List, Comparator) sort(List, Comparator)} * method), prior to making this call. If it is * not sorted, the results are undefined. If the list contains multiple * elements equal to the specified object, there is no guarantee which one * will be found. * * <p>This method runs in log(n) time for a "random access" list (which * provides near-constant-time positional access). If the specified list * does not implement the {@link RandomAccess} interface and is large, * this method will do an iterator-based binary search that performs * O(n) link traversals and O(log n) element comparisons. * * @param <T> the class of the objects in the list * @param list the list to be searched. * @param key the key to be searched for. * @param c the comparator by which the list is ordered. * A {@code null} value indicates that the elements' * {@linkplain Comparable natural ordering} should be used. * @return the index of the search key, if it is contained in the list; * otherwise, <code>(-(<i>insertion point</i>) - 1)</code>. The * <i>insertion point</i> is defined as the point at which the * key would be inserted into the list: the index of the first * element greater than the key, or {@code list.size()} if all * elements in the list are less than the specified key. Note * that this guarantees that the return value will be >= 0 if * and only if the key is found. * @throws ClassCastException if the list contains elements that are not * <i>mutually comparable</i> using the specified comparator, * or the search key is not mutually comparable with the * elements of the list using this comparator. */ @SuppressWarnings("unchecked") public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) { if (c == null) return binarySearch((List<? extends Comparable<? super T>>) list, key); if (list instanceof RandomAccess || list.size() < BINARYSEARCH_THRESHOLD) return Collections.indexedBinarySearch(list, key, c); else return Collections.iteratorBinarySearch(list, key, c); } private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { int low = 0; int high = l.size() - 1; while (low <= high) { int mid = (low + high) >>> 1; T midVal = l.get(mid); int cmp = c.compare(midVal, key); if (cmp < 0) low = mid + 1; else if (cmp > 0) high = mid - 1; else return mid; // key found } return -(low + 1); // key not found } private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) { int low = 0; int high = l.size() - 1; ListIterator<? extends T> i = l.listIterator(); while (low <= high) { int mid = (low + high) >>> 1; T midVal = get(i, mid); int cmp = c.compare(midVal, key); if (cmp < 0) low = mid + 1; else if (cmp > 0) high = mid - 1; else return mid; // key found } return -(low + 1); // key not found } /** * Reverses the order of the elements in the specified list.<p> * * This method runs in linear time. * * @param list the list whose elements are to be reversed. * @throws UnsupportedOperationException if the specified list or * its list-iterator does not support the {@code set} operation. */ @SuppressWarnings({ "rawtypes", "unchecked" }) public static void reverse(List<?> list) { int size = list.size(); if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) { for (int i = 0, mid = size >> 1, j = size - 1; i < mid; i++, j--) swap(list, i, j); } else { // instead of using a raw type here, it's possible to capture // the wildcard but it will require a call to a supplementary // private method ListIterator fwd = list.listIterator(); ListIterator rev = list.listIterator(size); for (int i = 0, mid = list.size() >> 1; i < mid; i++) { Object tmp = fwd.next(); fwd.set(rev.previous()); rev.set(tmp); } } } /** * Randomly permutes the specified list using a default source of * randomness. All permutations occur with approximately equal * likelihood. * * <p>The hedge "approximately" is used in the foregoing description because * default source of randomness is only approximately an unbiased source * of independently chosen bits. If it were a perfect source of randomly * chosen bits, then the algorithm would choose permutations with perfect * uniformity. * * <p>This implementation traverses the list backwards, from the last * element up to the second, repeatedly swapping a randomly selected element * into the "current position". Elements are randomly selected from the * portion of the list that runs from the first element to the current * position, inclusive. * * <p>This method runs in linear time. If the specified list does not * implement the {@link RandomAccess} interface and is large, this * implementation dumps the specified list into an array before shuffling * it, and dumps the shuffled array back into the list. This avoids the * quadratic behavior that would result from shuffling a "sequential * access" list in place. * * @param list the list to be shuffled. * @throws UnsupportedOperationException if the specified list or * its list-iterator does not support the {@code set} operation. */ public static void shuffle(List<?> list) { Random rnd = r; if (rnd == null) r = rnd = new Random(); // harmless race. shuffle(list, rnd); } private static Random r; /** * Randomly permute the specified list using the specified source of * randomness. All permutations occur with equal likelihood * assuming that the source of randomness is fair.<p> * * This implementation traverses the list backwards, from the last element * up to the second, repeatedly swapping a randomly selected element into * the "current position". Elements are randomly selected from the * portion of the list that runs from the first element to the current * position, inclusive.<p> * * This method runs in linear time. If the specified list does not * implement the {@link RandomAccess} interface and is large, this * implementation dumps the specified list into an array before shuffling * it, and dumps the shuffled array back into the list. This avoids the * quadratic behavior that would result from shuffling a "sequential * access" list in place. * * @param list the list to be shuffled. * @param rnd the source of randomness to use to shuffle the list. * @throws UnsupportedOperationException if the specified list or its * list-iterator does not support the {@code set} operation. */ @SuppressWarnings({ "rawtypes", "unchecked" }) public static void shuffle(List<?> list, Random rnd) { int size = list.size(); if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) { for (int i = size; i > 1; i--) swap(list, i - 1, rnd.nextInt(i)); } else { Object[] arr = list.toArray(); // Shuffle array for (int i = size; i > 1; i--) swap(arr, i - 1, rnd.nextInt(i)); // Dump array back into list // instead of using a raw type here, it's possible to capture // the wildcard but it will require a call to a supplementary // private method ListIterator it = list.listIterator(); for (Object e : arr) { it.next(); it.set(e); } } } /** * Swaps the elements at the specified positions in the specified list. * (If the specified positions are equal, invoking this method leaves * the list unchanged.) * * @param list The list in which to swap elements. * @param i the index of one element to be swapped. * @param j the index of the other element to be swapped. * @throws IndexOutOfBoundsException if either {@code i} or {@code j} * is out of range (i < 0 || i >= list.size() * || j < 0 || j >= list.size()). * @since 1.4 */ @SuppressWarnings({ "rawtypes", "unchecked" }) public static void swap(List<?> list, int i, int j) { // instead of using a raw type here, it's possible to capture // the wildcard but it will require a call to a supplementary // private method final List l = list; l.set(i, l.set(j, l.get(i))); } /** * Swaps the two specified elements in the specified array. */ private static void swap(Object[] arr, int i, int j) { Object tmp = arr[i]; arr[i] = arr[j]; arr[j] = tmp; } /** * Replaces all of the elements of the specified list with the specified * element. <p> * * This method runs in linear time. * * @param <T> the class of the objects in the list * @param list the list to be filled with the specified element. * @param obj The element with which to fill the specified list. * @throws UnsupportedOperationException if the specified list or its * list-iterator does not support the {@code set} operation. */ public static <T> void fill(List<? super T> list, T obj) { int size = list.size(); if (size < FILL_THRESHOLD || list instanceof RandomAccess) { for (int i = 0; i < size; i++) list.set(i, obj); } else { ListIterator<? super T> itr = list.listIterator(); for (int i = 0; i < size; i++) { itr.next(); itr.set(obj); } } } /** * Copies all of the elements from one list into another. After the * operation, the index of each copied element in the destination list * will be identical to its index in the source list. The destination * list's size must be greater than or equal to the source list's size. * If it is greater, the remaining elements in the destination list are * unaffected. <p> * * This method runs in linear time. * * @param <T> the class of the objects in the lists * @param dest The destination list. * @param src The source list. * @throws IndexOutOfBoundsException if the destination list is too small * to contain the entire source List. * @throws UnsupportedOperationException if the destination list's * list-iterator does not support the {@code set} operation. */ public static <T> void copy(List<? super T> dest, List<? extends T> src) { int srcSize = src.size(); if (srcSize > dest.size()) throw new IndexOutOfBoundsException("Source does not fit in dest"); if (srcSize < COPY_THRESHOLD || (src instanceof RandomAccess && dest instanceof RandomAccess)) { for (int i = 0; i < srcSize; i++) dest.set(i, src.get(i)); } else { ListIterator<? super T> di = dest.listIterator(); ListIterator<? extends T> si = src.listIterator(); for (int i = 0; i < srcSize; i++) { di.next(); di.set(si.next()); } } } /** * Returns the minimum element of the given collection, according to the * <i>natural ordering</i> of its elements. All elements in the * collection must implement the {@code Comparable} interface. * Furthermore, all elements in the collection must be <i>mutually * comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a * {@code ClassCastException} for any elements {@code e1} and * {@code e2} in the collection).<p> * * This method iterates over the entire collection, hence it requires * time proportional to the size of the collection. * * @param <T> the class of the objects in the collection * @param coll the collection whose minimum element is to be determined. * @return the minimum element of the given collection, according * to the <i>natural ordering</i> of its elements. * @throws ClassCastException if the collection contains elements that are * not <i>mutually comparable</i> (for example, strings and * integers). * @throws NoSuchElementException if the collection is empty. * @see Comparable */ public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) { Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (next.compareTo(candidate) < 0) candidate = next; } return candidate; } /** * Returns the minimum element of the given collection, according to the * order induced by the specified comparator. All elements in the * collection must be <i>mutually comparable</i> by the specified * comparator (that is, {@code comp.compare(e1, e2)} must not throw a * {@code ClassCastException} for any elements {@code e1} and * {@code e2} in the collection).<p> * * This method iterates over the entire collection, hence it requires * time proportional to the size of the collection. * * @param <T> the class of the objects in the collection * @param coll the collection whose minimum element is to be determined. * @param comp the comparator with which to determine the minimum element. * A {@code null} value indicates that the elements' <i>natural * ordering</i> should be used. * @return the minimum element of the given collection, according * to the specified comparator. * @throws ClassCastException if the collection contains elements that are * not <i>mutually comparable</i> using the specified comparator. * @throws NoSuchElementException if the collection is empty. * @see Comparable */ @SuppressWarnings({ "unchecked", "rawtypes" }) public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) { if (comp == null) return (T) min((Collection) coll); Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (comp.compare(next, candidate) < 0) candidate = next; } return candidate; } /** * Returns the maximum element of the given collection, according to the * <i>natural ordering</i> of its elements. All elements in the * collection must implement the {@code Comparable} interface. * Furthermore, all elements in the collection must be <i>mutually * comparable</i> (that is, {@code e1.compareTo(e2)} must not throw a * {@code ClassCastException} for any elements {@code e1} and * {@code e2} in the collection).<p> * * This method iterates over the entire collection, hence it requires * time proportional to the size of the collection. * * @param <T> the class of the objects in the collection * @param coll the collection whose maximum element is to be determined. * @return the maximum element of the given collection, according * to the <i>natural ordering</i> of its elements. * @throws ClassCastException if the collection contains elements that are * not <i>mutually comparable</i> (for example, strings and * integers). * @throws NoSuchElementException if the collection is empty. * @see Comparable */ public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (next.compareTo(candidate) > 0) candidate = next; } return candidate; } /** * Returns the maximum element of the given collection, according to the * order induced by the specified comparator. All elements in the * collection must be <i>mutually comparable</i> by the specified * comparator (that is, {@code comp.compare(e1, e2)} must not throw a * {@code ClassCastException} for any elements {@code e1} and * {@code e2} in the collection).<p> * * This method iterates over the entire collection, hence it requires * time proportional to the size of the collection. * * @param <T> the class of the objects in the collection * @param coll the collection whose maximum element is to be determined. * @param comp the comparator with which to determine the maximum element. * A {@code null} value indicates that the elements' <i>natural * ordering</i> should be used. * @return the maximum element of the given collection, according * to the specified comparator. * @throws ClassCastException if the collection contains elements that are * not <i>mutually comparable</i> using the specified comparator. * @throws NoSuchElementException if the collection is empty. * @see Comparable */ @SuppressWarnings({ "unchecked", "rawtypes" }) public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) { if (comp == null) return (T) max((Collection) coll); Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (comp.compare(next, candidate) > 0) candidate = next; } return candidate; } /** * Rotates the elements in the specified list by the specified distance. * After calling this method, the element at index {@code i} will be * the element previously at index {@code (i - distance)} mod * {@code list.size()}, for all values of {@code i} between {@code 0} * and {@code list.size()-1}, inclusive. (This method has no effect on * the size of the list.) * * <p>For example, suppose {@code list} comprises{@code [t, a, n, k, s]}. * After invoking {@code Collections.rotate(list, 1)} (or * {@code Collections.rotate(list, -4)}), {@code list} will comprise * {@code [s, t, a, n, k]}. * * <p>Note that this method can usefully be applied to sublists to * move one or more elements within a list while preserving the * order of the remaining elements. For example, the following idiom * moves the element at index {@code j} forward to position * {@code k} (which must be greater than or equal to {@code j}): * <pre> * Collections.rotate(list.subList(j, k+1), -1); * </pre> * To make this concrete, suppose {@code list} comprises * {@code [a, b, c, d, e]}. To move the element at index {@code 1} * ({@code b}) forward two positions, perform the following invocation: * <pre> * Collections.rotate(l.subList(1, 4), -1); * </pre> * The resulting list is {@code [a, c, d, b, e]}. * * <p>To move more than one element forward, increase the absolute value * of the rotation distance. To move elements backward, use a positive * shift distance. * * <p>If the specified list is small or implements the {@link * RandomAccess} interface, this implementation exchanges the first * element into the location it should go, and then repeatedly exchanges * the displaced element into the location it should go until a displaced * element is swapped into the first element. If necessary, the process * is repeated on the second and successive elements, until the rotation * is complete. If the specified list is large and doesn't implement the * {@code RandomAccess} interface, this implementation breaks the * list into two sublist views around index {@code -distance mod size}. * Then the {@link #reverse(List)} method is invoked on each sublist view, * and finally it is invoked on the entire list. For a more complete * description of both algorithms, see Section 2.3 of Jon Bentley's * <i>Programming Pearls</i> (Addison-Wesley, 1986). * * @param list the list to be rotated. * @param distance the distance to rotate the list. There are no * constraints on this value; it may be zero, negative, or * greater than {@code list.size()}. * @throws UnsupportedOperationException if the specified list or * its list-iterator does not support the {@code set} operation. * @since 1.4 */ public static void rotate(List<?> list, int distance) { if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD) rotate1(list, distance); else rotate2(list, distance); } private static <T> void rotate1(List<T> list, int distance) { int size = list.size(); if (size == 0) return; distance = distance % size; if (distance < 0) distance += size; if (distance == 0) return; for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) { T displaced = list.get(cycleStart); int i = cycleStart; do { i += distance; if (i >= size) i -= size; displaced = list.set(i, displaced); nMoved++; } while (i != cycleStart); } } private static void rotate2(List<?> list, int distance) { int size = list.size(); if (size == 0) return; int mid = -distance % size; if (mid < 0) mid += size; if (mid == 0) return; reverse(list.subList(0, mid)); reverse(list.subList(mid, size)); reverse(list); } /** * Replaces all occurrences of one specified value in a list with another. * More formally, replaces with {@code newVal} each element {@code e} * in {@code list} such that * {@code (oldVal==null ? e==null : oldVal.equals(e))}. * (This method has no effect on the size of the list.) * * @param <T> the class of the objects in the list * @param list the list in which replacement is to occur. * @param oldVal the old value to be replaced. * @param newVal the new value with which {@code oldVal} is to be * replaced. * @return {@code true} if {@code list} contained one or more elements * {@code e} such that * {@code (oldVal==null ? e==null : oldVal.equals(e))}. * @throws UnsupportedOperationException if the specified list or * its list-iterator does not support the {@code set} operation. * @since 1.4 */ public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) { boolean result = false; int size = list.size(); if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) { if (oldVal == null) { for (int i = 0; i < size; i++) { if (list.get(i) == null) { list.set(i, newVal); result = true; } } } else { for (int i = 0; i < size; i++) { if (oldVal.equals(list.get(i))) { list.set(i, newVal); result = true; } } } } else { ListIterator<T> itr = list.listIterator(); if (oldVal == null) { for (int i = 0; i < size; i++) { if (itr.next() == null) { itr.set(newVal); result = true; } } } else { for (int i = 0; i < size; i++) { if (oldVal.equals(itr.next())) { itr.set(newVal); result = true; } } } } return result; } /** * Returns the starting position of the first occurrence of the specified * target list within the specified source list, or -1 if there is no * such occurrence. More formally, returns the lowest index {@code i} * such that {@code source.subList(i, i+target.size()).equals(target)}, * or -1 if there is no such index. (Returns -1 if * {@code target.size() > source.size()}) * * <p>This implementation uses the "brute force" technique of scanning * over the source list, looking for a match with the target at each * location in turn. * * @param source the list in which to search for the first occurrence * of {@code target}. * @param target the list to search for as a subList of {@code source}. * @return the starting position of the first occurrence of the specified * target list within the specified source list, or -1 if there * is no such occurrence. * @since 1.4 */ public static int indexOfSubList(List<?> source, List<?> target) { int sourceSize = source.size(); int targetSize = target.size(); int maxCandidate = sourceSize - targetSize; if (sourceSize < INDEXOFSUBLIST_THRESHOLD || (source instanceof RandomAccess && target instanceof RandomAccess)) { nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) { for (int i = 0, j = candidate; i < targetSize; i++, j++) if (!eq(target.get(i), source.get(j))) continue nextCand; // Element mismatch, try next cand return candidate; // All elements of candidate matched target } } else { // Iterator version of above algorithm ListIterator<?> si = source.listIterator(); nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) { ListIterator<?> ti = target.listIterator(); for (int i = 0; i < targetSize; i++) { if (!eq(ti.next(), si.next())) { // Back up source iterator to next candidate for (int j = 0; j < i; j++) si.previous(); continue nextCand; } } return candidate; } } return -1; // No candidate matched the target } /** * Returns the starting position of the last occurrence of the specified * target list within the specified source list, or -1 if there is no such * occurrence. More formally, returns the highest index {@code i} * such that {@code source.subList(i, i+target.size()).equals(target)}, * or -1 if there is no such index. (Returns -1 if * {@code target.size() > source.size()}) * * <p>This implementation uses the "brute force" technique of iterating * over the source list, looking for a match with the target at each * location in turn. * * @param source the list in which to search for the last occurrence * of {@code target}. * @param target the list to search for as a subList of {@code source}. * @return the starting position of the last occurrence of the specified * target list within the specified source list, or -1 if there * is no such occurrence. * @since 1.4 */ public static int lastIndexOfSubList(List<?> source, List<?> target) { int sourceSize = source.size(); int targetSize = target.size(); int maxCandidate = sourceSize - targetSize; if (sourceSize < INDEXOFSUBLIST_THRESHOLD || source instanceof RandomAccess) { // Index access version nextCand: for (int candidate = maxCandidate; candidate >= 0; candidate--) { for (int i = 0, j = candidate; i < targetSize; i++, j++) if (!eq(target.get(i), source.get(j))) continue nextCand; // Element mismatch, try next cand return candidate; // All elements of candidate matched target } } else { // Iterator version of above algorithm if (maxCandidate < 0) return -1; ListIterator<?> si = source.listIterator(maxCandidate); nextCand: for (int candidate = maxCandidate; candidate >= 0; candidate--) { ListIterator<?> ti = target.listIterator(); for (int i = 0; i < targetSize; i++) { if (!eq(ti.next(), si.next())) { if (candidate != 0) { // Back up source iterator to next candidate for (int j = 0; j <= i + 1; j++) si.previous(); } continue nextCand; } } return candidate; } } return -1; // No candidate matched the target } // Unmodifiable Wrappers /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified collection. Query operations on the returned collection "read through" * to the specified collection, and attempts to modify the returned * collection, whether direct or via its iterator, result in an * {@code UnsupportedOperationException}.<p> * * The returned collection does <i>not</i> pass the hashCode and equals * operations through to the backing collection, but relies on * {@code Object}'s {@code equals} and {@code hashCode} methods. This * is necessary to preserve the contracts of these operations in the case * that the backing collection is a set or a list.<p> * * The returned collection will be serializable if the specified collection * is serializable. * * @param <T> the class of the objects in the collection * @param c the collection for which an unmodifiable view is to be * returned. * @return an unmodifiable view of the specified collection. */ public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) { return new UnmodifiableCollection<>(c); } /** * @serial include */ static class UnmodifiableCollection<E> implements Collection<E>, Serializable { private static final long serialVersionUID = 1820017752578914078L; final Collection<? extends E> c; UnmodifiableCollection(Collection<? extends E> c) { if (c == null) throw new NullPointerException(); this.c = c; } public int size() { return c.size(); } public boolean isEmpty() { return c.isEmpty(); } public boolean contains(Object o) { return c.contains(o); } public Object[] toArray() { return c.toArray(); } public <T> T[] toArray(T[] a) { return c.toArray(a); } public <T> T[] toArray(IntFunction<T[]> f) { return c.toArray(f); } public String toString() { return c.toString(); } public Iterator<E> iterator() { return new Iterator<E>() { private final Iterator<? extends E> i = c.iterator(); public boolean hasNext() { return i.hasNext(); } public E next() { return i.next(); } public void remove() { throw new UnsupportedOperationException(); } @Override public void forEachRemaining(Consumer<? super E> action) { // Use backing collection version i.forEachRemaining(action); } }; } public boolean add(E e) { throw new UnsupportedOperationException(); } public boolean remove(Object o) { throw new UnsupportedOperationException(); } public boolean containsAll(Collection<?> coll) { return c.containsAll(coll); } public boolean addAll(Collection<? extends E> coll) { throw new UnsupportedOperationException(); } public boolean removeAll(Collection<?> coll) { throw new UnsupportedOperationException(); } public boolean retainAll(Collection<?> coll) { throw new UnsupportedOperationException(); } public void clear() { throw new UnsupportedOperationException(); } // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { c.forEach(action); } @Override public boolean removeIf(Predicate<? super E> filter) { throw new UnsupportedOperationException(); } @SuppressWarnings("unchecked") @Override public Spliterator<E> spliterator() { return (Spliterator<E>) c.spliterator(); } @SuppressWarnings("unchecked") @Override public Stream<E> stream() { return (Stream<E>) c.stream(); } @SuppressWarnings("unchecked") @Override public Stream<E> parallelStream() { return (Stream<E>) c.parallelStream(); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified set. Query operations on the returned set "read through" to the specified * set, and attempts to modify the returned set, whether direct or via its * iterator, result in an {@code UnsupportedOperationException}.<p> * * The returned set will be serializable if the specified set * is serializable. * * @param <T> the class of the objects in the set * @param s the set for which an unmodifiable view is to be returned. * @return an unmodifiable view of the specified set. */ public static <T> Set<T> unmodifiableSet(Set<? extends T> s) { return new UnmodifiableSet<>(s); } /** * @serial include */ static class UnmodifiableSet<E> extends UnmodifiableCollection<E> implements Set<E>, Serializable { private static final long serialVersionUID = -9215047833775013803L; UnmodifiableSet(Set<? extends E> s) { super(s); } public boolean equals(Object o) { return o == this || c.equals(o); } public int hashCode() { return c.hashCode(); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified sorted set. Query operations on the returned sorted set "read * through" to the specified sorted set. Attempts to modify the returned * sorted set, whether direct, via its iterator, or via its * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in * an {@code UnsupportedOperationException}.<p> * * The returned sorted set will be serializable if the specified sorted set * is serializable. * * @param <T> the class of the objects in the set * @param s the sorted set for which an unmodifiable view is to be * returned. * @return an unmodifiable view of the specified sorted set. */ public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) { return new UnmodifiableSortedSet<>(s); } /** * @serial include */ static class UnmodifiableSortedSet<E> extends UnmodifiableSet<E> implements SortedSet<E>, Serializable { private static final long serialVersionUID = -4929149591599911165L; private final SortedSet<E> ss; UnmodifiableSortedSet(SortedSet<E> s) { super(s); ss = s; } public Comparator<? super E> comparator() { return ss.comparator(); } public SortedSet<E> subSet(E fromElement, E toElement) { return new UnmodifiableSortedSet<>(ss.subSet(fromElement, toElement)); } public SortedSet<E> headSet(E toElement) { return new UnmodifiableSortedSet<>(ss.headSet(toElement)); } public SortedSet<E> tailSet(E fromElement) { return new UnmodifiableSortedSet<>(ss.tailSet(fromElement)); } public E first() { return ss.first(); } public E last() { return ss.last(); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified navigable set. Query operations on the returned navigable set "read * through" to the specified navigable set. Attempts to modify the returned * navigable set, whether direct, via its iterator, or via its * {@code subSet}, {@code headSet}, or {@code tailSet} views, result in * an {@code UnsupportedOperationException}.<p> * * The returned navigable set will be serializable if the specified * navigable set is serializable. * * @param <T> the class of the objects in the set * @param s the navigable set for which an unmodifiable view is to be * returned * @return an unmodifiable view of the specified navigable set * @since 1.8 */ public static <T> NavigableSet<T> unmodifiableNavigableSet(NavigableSet<T> s) { return new UnmodifiableNavigableSet<>(s); } /** * Wraps a navigable set and disables all of the mutative operations. * * @param <E> type of elements * @serial include */ static class UnmodifiableNavigableSet<E> extends UnmodifiableSortedSet<E> implements NavigableSet<E>, Serializable { private static final long serialVersionUID = -6027448201786391929L; /** * A singleton empty unmodifiable navigable set used for * {@link #emptyNavigableSet()}. * * @param <E> type of elements, if there were any, and bounds */ private static class EmptyNavigableSet<E> extends UnmodifiableNavigableSet<E> implements Serializable { private static final long serialVersionUID = -6291252904449939134L; public EmptyNavigableSet() { super(new TreeSet<>()); } private Object readResolve() { return EMPTY_NAVIGABLE_SET; } } @SuppressWarnings("rawtypes") private static final NavigableSet<?> EMPTY_NAVIGABLE_SET = new EmptyNavigableSet<>(); /** * The instance we are protecting. */ private final NavigableSet<E> ns; UnmodifiableNavigableSet(NavigableSet<E> s) { super(s); ns = s; } public E lower(E e) { return ns.lower(e); } public E floor(E e) { return ns.floor(e); } public E ceiling(E e) { return ns.ceiling(e); } public E higher(E e) { return ns.higher(e); } public E pollFirst() { throw new UnsupportedOperationException(); } public E pollLast() { throw new UnsupportedOperationException(); } public NavigableSet<E> descendingSet() { return new UnmodifiableNavigableSet<>(ns.descendingSet()); } public Iterator<E> descendingIterator() { return descendingSet().iterator(); } public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return new UnmodifiableNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive)); } public NavigableSet<E> headSet(E toElement, boolean inclusive) { return new UnmodifiableNavigableSet<>(ns.headSet(toElement, inclusive)); } public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { return new UnmodifiableNavigableSet<>(ns.tailSet(fromElement, inclusive)); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified list. Query operations on the returned list "read through" to the * specified list, and attempts to modify the returned list, whether * direct or via its iterator, result in an * {@code UnsupportedOperationException}.<p> * * The returned list will be serializable if the specified list * is serializable. Similarly, the returned list will implement * {@link RandomAccess} if the specified list does. * * @param <T> the class of the objects in the list * @param list the list for which an unmodifiable view is to be returned. * @return an unmodifiable view of the specified list. */ public static <T> List<T> unmodifiableList(List<? extends T> list) { return (list instanceof RandomAccess ? new UnmodifiableRandomAccessList<>(list) : new UnmodifiableList<>(list)); } /** * @serial include */ static class UnmodifiableList<E> extends UnmodifiableCollection<E> implements List<E> { private static final long serialVersionUID = -283967356065247728L; final List<? extends E> list; UnmodifiableList(List<? extends E> list) { super(list); this.list = list; } public boolean equals(Object o) { return o == this || list.equals(o); } public int hashCode() { return list.hashCode(); } public E get(int index) { return list.get(index); } public E set(int index, E element) { throw new UnsupportedOperationException(); } public void add(int index, E element) { throw new UnsupportedOperationException(); } public E remove(int index) { throw new UnsupportedOperationException(); } public int indexOf(Object o) { return list.indexOf(o); } public int lastIndexOf(Object o) { return list.lastIndexOf(o); } public boolean addAll(int index, Collection<? extends E> c) { throw new UnsupportedOperationException(); } @Override public void replaceAll(UnaryOperator<E> operator) { throw new UnsupportedOperationException(); } @Override public void sort(Comparator<? super E> c) { throw new UnsupportedOperationException(); } public ListIterator<E> listIterator() { return listIterator(0); } public ListIterator<E> listIterator(final int index) { return new ListIterator<E>() { private final ListIterator<? extends E> i = list.listIterator(index); public boolean hasNext() { return i.hasNext(); } public E next() { return i.next(); } public boolean hasPrevious() { return i.hasPrevious(); } public E previous() { return i.previous(); } public int nextIndex() { return i.nextIndex(); } public int previousIndex() { return i.previousIndex(); } public void remove() { throw new UnsupportedOperationException(); } public void set(E e) { throw new UnsupportedOperationException(); } public void add(E e) { throw new UnsupportedOperationException(); } @Override public void forEachRemaining(Consumer<? super E> action) { i.forEachRemaining(action); } }; } public List<E> subList(int fromIndex, int toIndex) { return new UnmodifiableList<>(list.subList(fromIndex, toIndex)); } /** * UnmodifiableRandomAccessList instances are serialized as * UnmodifiableList instances to allow them to be deserialized * in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList). * This method inverts the transformation. As a beneficial * side-effect, it also grafts the RandomAccess marker onto * UnmodifiableList instances that were serialized in pre-1.4 JREs. * * Note: Unfortunately, UnmodifiableRandomAccessList instances * serialized in 1.4.1 and deserialized in 1.4 will become * UnmodifiableList instances, as this method was missing in 1.4. */ private Object readResolve() { return (list instanceof RandomAccess ? new UnmodifiableRandomAccessList<>(list) : this); } } /** * @serial include */ static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E> implements RandomAccess { UnmodifiableRandomAccessList(List<? extends E> list) { super(list); } public List<E> subList(int fromIndex, int toIndex) { return new UnmodifiableRandomAccessList<>(list.subList(fromIndex, toIndex)); } private static final long serialVersionUID = -2542308836966382001L; /** * Allows instances to be deserialized in pre-1.4 JREs (which do * not have UnmodifiableRandomAccessList). UnmodifiableList has * a readResolve method that inverts this transformation upon * deserialization. */ private Object writeReplace() { return new UnmodifiableList<>(list); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified map. Query operations on the returned map "read through" * to the specified map, and attempts to modify the returned * map, whether direct or via its collection views, result in an * {@code UnsupportedOperationException}.<p> * * The returned map will be serializable if the specified map * is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the map for which an unmodifiable view is to be returned. * @return an unmodifiable view of the specified map. */ public static <K, V> Map<K, V> unmodifiableMap(Map<? extends K, ? extends V> m) { return new UnmodifiableMap<>(m); } /** * @serial include */ private static class UnmodifiableMap<K, V> implements Map<K, V>, Serializable { private static final long serialVersionUID = -1034234728574286014L; private final Map<? extends K, ? extends V> m; UnmodifiableMap(Map<? extends K, ? extends V> m) { if (m == null) throw new NullPointerException(); this.m = m; } public int size() { return m.size(); } public boolean isEmpty() { return m.isEmpty(); } public boolean containsKey(Object key) { return m.containsKey(key); } public boolean containsValue(Object val) { return m.containsValue(val); } public V get(Object key) { return m.get(key); } public V put(K key, V value) { throw new UnsupportedOperationException(); } public V remove(Object key) { throw new UnsupportedOperationException(); } public void putAll(Map<? extends K, ? extends V> m) { throw new UnsupportedOperationException(); } public void clear() { throw new UnsupportedOperationException(); } private transient Set<K> keySet; private transient Set<Map.Entry<K, V>> entrySet; private transient Collection<V> values; public Set<K> keySet() { if (keySet == null) keySet = unmodifiableSet(m.keySet()); return keySet; } public Set<Map.Entry<K, V>> entrySet() { if (entrySet == null) entrySet = new UnmodifiableEntrySet<>(m.entrySet()); return entrySet; } public Collection<V> values() { if (values == null) values = unmodifiableCollection(m.values()); return values; } public boolean equals(Object o) { return o == this || m.equals(o); } public int hashCode() { return m.hashCode(); } public String toString() { return m.toString(); } // Override default methods in Map @Override @SuppressWarnings("unchecked") public V getOrDefault(Object k, V defaultValue) { // Safe cast as we don't change the value return ((Map<K, V>) m).getOrDefault(k, defaultValue); } @Override public void forEach(BiConsumer<? super K, ? super V> action) { m.forEach(action); } @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { throw new UnsupportedOperationException(); } @Override public V putIfAbsent(K key, V value) { throw new UnsupportedOperationException(); } @Override public boolean remove(Object key, Object value) { throw new UnsupportedOperationException(); } @Override public boolean replace(K key, V oldValue, V newValue) { throw new UnsupportedOperationException(); } @Override public V replace(K key, V value) { throw new UnsupportedOperationException(); } @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { throw new UnsupportedOperationException(); } @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } /** * We need this class in addition to UnmodifiableSet as * Map.Entries themselves permit modification of the backing Map * via their setValue operation. This class is subtle: there are * many possible attacks that must be thwarted. * * @serial include */ static class UnmodifiableEntrySet<K, V> extends UnmodifiableSet<Map.Entry<K, V>> { private static final long serialVersionUID = 7854390611657943733L; @SuppressWarnings({ "unchecked", "rawtypes" }) UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) { // Need to cast to raw in order to work around a limitation in the type system super((Set) s); } static <K, V> Consumer<Map.Entry<? extends K, ? extends V>> entryConsumer( Consumer<? super Entry<K, V>> action) { return e -> action.accept(new UnmodifiableEntry<>(e)); } public void forEach(Consumer<? super Entry<K, V>> action) { Objects.requireNonNull(action); c.forEach(entryConsumer(action)); } static final class UnmodifiableEntrySetSpliterator<K, V> implements Spliterator<Entry<K, V>> { final Spliterator<Map.Entry<K, V>> s; UnmodifiableEntrySetSpliterator(Spliterator<Entry<K, V>> s) { this.s = s; } @Override public boolean tryAdvance(Consumer<? super Entry<K, V>> action) { Objects.requireNonNull(action); return s.tryAdvance(entryConsumer(action)); } @Override public void forEachRemaining(Consumer<? super Entry<K, V>> action) { Objects.requireNonNull(action); s.forEachRemaining(entryConsumer(action)); } @Override public Spliterator<Entry<K, V>> trySplit() { Spliterator<Entry<K, V>> split = s.trySplit(); return split == null ? null : new UnmodifiableEntrySetSpliterator<>(split); } @Override public long estimateSize() { return s.estimateSize(); } @Override public long getExactSizeIfKnown() { return s.getExactSizeIfKnown(); } @Override public int characteristics() { return s.characteristics(); } @Override public boolean hasCharacteristics(int characteristics) { return s.hasCharacteristics(characteristics); } @Override public Comparator<? super Entry<K, V>> getComparator() { return s.getComparator(); } } @SuppressWarnings("unchecked") public Spliterator<Entry<K, V>> spliterator() { return new UnmodifiableEntrySetSpliterator<>((Spliterator<Map.Entry<K, V>>) c.spliterator()); } @Override public Stream<Entry<K, V>> stream() { return StreamSupport.stream(spliterator(), false); } @Override public Stream<Entry<K, V>> parallelStream() { return StreamSupport.stream(spliterator(), true); } public Iterator<Map.Entry<K, V>> iterator() { return new Iterator<Map.Entry<K, V>>() { private final Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator(); public boolean hasNext() { return i.hasNext(); } public Map.Entry<K, V> next() { return new UnmodifiableEntry<>(i.next()); } public void remove() { throw new UnsupportedOperationException(); } public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { i.forEachRemaining(entryConsumer(action)); } }; } @SuppressWarnings("unchecked") public Object[] toArray() { Object[] a = c.toArray(); for (int i = 0; i < a.length; i++) a[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>) a[i]); return a; } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { // We don't pass a to c.toArray, to avoid window of // vulnerability wherein an unscrupulous multithreaded client // could get his hands on raw (unwrapped) Entries from c. Object[] arr = c.toArray(a.length == 0 ? a : Arrays.copyOf(a, 0)); for (int i = 0; i < arr.length; i++) arr[i] = new UnmodifiableEntry<>((Map.Entry<? extends K, ? extends V>) arr[i]); if (arr.length > a.length) return (T[]) arr; System.arraycopy(arr, 0, a, 0, arr.length); if (a.length > arr.length) a[arr.length] = null; return a; } /** * This method is overridden to protect the backing set against * an object with a nefarious equals function that senses * that the equality-candidate is Map.Entry and calls its * setValue method. */ public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; return c.contains(new UnmodifiableEntry<>((Map.Entry<?, ?>) o)); } /** * The next two methods are overridden to protect against * an unscrupulous List whose contains(Object o) method senses * when o is a Map.Entry, and calls o.setValue. */ public boolean containsAll(Collection<?> coll) { for (Object e : coll) { if (!contains(e)) // Invokes safe contains() above return false; } return true; } public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof Set)) return false; Set<?> s = (Set<?>) o; if (s.size() != c.size()) return false; return containsAll(s); // Invokes safe containsAll() above } /** * This "wrapper class" serves two purposes: it prevents * the client from modifying the backing Map, by short-circuiting * the setValue method, and it protects the backing Map against * an ill-behaved Map.Entry that attempts to modify another * Map Entry when asked to perform an equality check. */ private static class UnmodifiableEntry<K, V> implements Map.Entry<K, V> { private Map.Entry<? extends K, ? extends V> e; UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) { this.e = Objects.requireNonNull(e); } public K getKey() { return e.getKey(); } public V getValue() { return e.getValue(); } public V setValue(V value) { throw new UnsupportedOperationException(); } public int hashCode() { return e.hashCode(); } public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Map.Entry)) return false; Map.Entry<?, ?> t = (Map.Entry<?, ?>) o; return eq(e.getKey(), t.getKey()) && eq(e.getValue(), t.getValue()); } public String toString() { return e.toString(); } } } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified sorted map. Query operations on the returned sorted map "read through" * to the specified sorted map. Attempts to modify the returned * sorted map, whether direct, via its collection views, or via its * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in * an {@code UnsupportedOperationException}.<p> * * The returned sorted map will be serializable if the specified sorted map * is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the sorted map for which an unmodifiable view is to be * returned. * @return an unmodifiable view of the specified sorted map. */ public static <K, V> SortedMap<K, V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) { return new UnmodifiableSortedMap<>(m); } /** * @serial include */ static class UnmodifiableSortedMap<K, V> extends UnmodifiableMap<K, V> implements SortedMap<K, V>, Serializable { private static final long serialVersionUID = -8806743815996713206L; private final SortedMap<K, ? extends V> sm; UnmodifiableSortedMap(SortedMap<K, ? extends V> m) { super(m); sm = m; } public Comparator<? super K> comparator() { return sm.comparator(); } public SortedMap<K, V> subMap(K fromKey, K toKey) { return new UnmodifiableSortedMap<>(sm.subMap(fromKey, toKey)); } public SortedMap<K, V> headMap(K toKey) { return new UnmodifiableSortedMap<>(sm.headMap(toKey)); } public SortedMap<K, V> tailMap(K fromKey) { return new UnmodifiableSortedMap<>(sm.tailMap(fromKey)); } public K firstKey() { return sm.firstKey(); } public K lastKey() { return sm.lastKey(); } } /** * Returns an <a href="Collection.html#unmodview">unmodifiable view</a> of the * specified navigable map. Query operations on the returned navigable map "read * through" to the specified navigable map. Attempts to modify the returned * navigable map, whether direct, via its collection views, or via its * {@code subMap}, {@code headMap}, or {@code tailMap} views, result in * an {@code UnsupportedOperationException}.<p> * * The returned navigable map will be serializable if the specified * navigable map is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the navigable map for which an unmodifiable view is to be * returned * @return an unmodifiable view of the specified navigable map * @since 1.8 */ public static <K, V> NavigableMap<K, V> unmodifiableNavigableMap(NavigableMap<K, ? extends V> m) { return new UnmodifiableNavigableMap<>(m); } /** * @serial include */ static class UnmodifiableNavigableMap<K, V> extends UnmodifiableSortedMap<K, V> implements NavigableMap<K, V>, Serializable { private static final long serialVersionUID = -4858195264774772197L; /** * A class for the {@link EMPTY_NAVIGABLE_MAP} which needs readResolve * to preserve singleton property. * * @param <K> type of keys, if there were any, and of bounds * @param <V> type of values, if there were any */ private static class EmptyNavigableMap<K, V> extends UnmodifiableNavigableMap<K, V> implements Serializable { private static final long serialVersionUID = -2239321462712562324L; EmptyNavigableMap() { super(new TreeMap<>()); } @Override public NavigableSet<K> navigableKeySet() { return emptyNavigableSet(); } private Object readResolve() { return EMPTY_NAVIGABLE_MAP; } } /** * Singleton for {@link emptyNavigableMap()} which is also immutable. */ private static final EmptyNavigableMap<?, ?> EMPTY_NAVIGABLE_MAP = new EmptyNavigableMap<>(); /** * The instance we wrap and protect. */ private final NavigableMap<K, ? extends V> nm; UnmodifiableNavigableMap(NavigableMap<K, ? extends V> m) { super(m); nm = m; } public K lowerKey(K key) { return nm.lowerKey(key); } public K floorKey(K key) { return nm.floorKey(key); } public K ceilingKey(K key) { return nm.ceilingKey(key); } public K higherKey(K key) { return nm.higherKey(key); } @SuppressWarnings("unchecked") public Entry<K, V> lowerEntry(K key) { Entry<K, V> lower = (Entry<K, V>) nm.lowerEntry(key); return (null != lower) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(lower) : null; } @SuppressWarnings("unchecked") public Entry<K, V> floorEntry(K key) { Entry<K, V> floor = (Entry<K, V>) nm.floorEntry(key); return (null != floor) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(floor) : null; } @SuppressWarnings("unchecked") public Entry<K, V> ceilingEntry(K key) { Entry<K, V> ceiling = (Entry<K, V>) nm.ceilingEntry(key); return (null != ceiling) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(ceiling) : null; } @SuppressWarnings("unchecked") public Entry<K, V> higherEntry(K key) { Entry<K, V> higher = (Entry<K, V>) nm.higherEntry(key); return (null != higher) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(higher) : null; } @SuppressWarnings("unchecked") public Entry<K, V> firstEntry() { Entry<K, V> first = (Entry<K, V>) nm.firstEntry(); return (null != first) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(first) : null; } @SuppressWarnings("unchecked") public Entry<K, V> lastEntry() { Entry<K, V> last = (Entry<K, V>) nm.lastEntry(); return (null != last) ? new UnmodifiableEntrySet.UnmodifiableEntry<>(last) : null; } public Entry<K, V> pollFirstEntry() { throw new UnsupportedOperationException(); } public Entry<K, V> pollLastEntry() { throw new UnsupportedOperationException(); } public NavigableMap<K, V> descendingMap() { return unmodifiableNavigableMap(nm.descendingMap()); } public NavigableSet<K> navigableKeySet() { return unmodifiableNavigableSet(nm.navigableKeySet()); } public NavigableSet<K> descendingKeySet() { return unmodifiableNavigableSet(nm.descendingKeySet()); } public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { return unmodifiableNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive)); } public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { return unmodifiableNavigableMap(nm.headMap(toKey, inclusive)); } public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { return unmodifiableNavigableMap(nm.tailMap(fromKey, inclusive)); } } // Synch Wrappers /** * Returns a synchronized (thread-safe) collection backed by the specified * collection. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing collection is accomplished * through the returned collection.<p> * * It is imperative that the user manually synchronize on the returned * collection when traversing it via {@link Iterator}, {@link Spliterator} * or {@link Stream}: * <pre> * Collection c = Collections.synchronizedCollection(myCollection); * ... * synchronized (c) { * Iterator i = c.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned collection does <i>not</i> pass the {@code hashCode} * and {@code equals} operations through to the backing collection, but * relies on {@code Object}'s equals and hashCode methods. This is * necessary to preserve the contracts of these operations in the case * that the backing collection is a set or a list.<p> * * The returned collection will be serializable if the specified collection * is serializable. * * @param <T> the class of the objects in the collection * @param c the collection to be "wrapped" in a synchronized collection. * @return a synchronized view of the specified collection. */ public static <T> Collection<T> synchronizedCollection(Collection<T> c) { return new SynchronizedCollection<>(c); } static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) { return new SynchronizedCollection<>(c, mutex); } /** * @serial include */ static class SynchronizedCollection<E> implements Collection<E>, Serializable { private static final long serialVersionUID = 3053995032091335093L; final Collection<E> c; // Backing Collection final Object mutex; // Object on which to synchronize SynchronizedCollection(Collection<E> c) { this.c = Objects.requireNonNull(c); mutex = this; } SynchronizedCollection(Collection<E> c, Object mutex) { this.c = Objects.requireNonNull(c); this.mutex = Objects.requireNonNull(mutex); } public int size() { synchronized (mutex) { return c.size(); } } public boolean isEmpty() { synchronized (mutex) { return c.isEmpty(); } } public boolean contains(Object o) { synchronized (mutex) { return c.contains(o); } } public Object[] toArray() { synchronized (mutex) { return c.toArray(); } } public <T> T[] toArray(T[] a) { synchronized (mutex) { return c.toArray(a); } } public <T> T[] toArray(IntFunction<T[]> f) { synchronized (mutex) { return c.toArray(f); } } public Iterator<E> iterator() { return c.iterator(); // Must be manually synched by user! } public boolean add(E e) { synchronized (mutex) { return c.add(e); } } public boolean remove(Object o) { synchronized (mutex) { return c.remove(o); } } public boolean containsAll(Collection<?> coll) { synchronized (mutex) { return c.containsAll(coll); } } public boolean addAll(Collection<? extends E> coll) { synchronized (mutex) { return c.addAll(coll); } } public boolean removeAll(Collection<?> coll) { synchronized (mutex) { return c.removeAll(coll); } } public boolean retainAll(Collection<?> coll) { synchronized (mutex) { return c.retainAll(coll); } } public void clear() { synchronized (mutex) { c.clear(); } } public String toString() { synchronized (mutex) { return c.toString(); } } // Override default methods in Collection @Override public void forEach(Consumer<? super E> consumer) { synchronized (mutex) { c.forEach(consumer); } } @Override public boolean removeIf(Predicate<? super E> filter) { synchronized (mutex) { return c.removeIf(filter); } } @Override public Spliterator<E> spliterator() { return c.spliterator(); // Must be manually synched by user! } @Override public Stream<E> stream() { return c.stream(); // Must be manually synched by user! } @Override public Stream<E> parallelStream() { return c.parallelStream(); // Must be manually synched by user! } private void writeObject(ObjectOutputStream s) throws IOException { synchronized (mutex) { s.defaultWriteObject(); } } } /** * Returns a synchronized (thread-safe) set backed by the specified * set. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing set is accomplished * through the returned set.<p> * * It is imperative that the user manually synchronize on the returned * collection when traversing it via {@link Iterator}, {@link Spliterator} * or {@link Stream}: * <pre> * Set s = Collections.synchronizedSet(new HashSet()); * ... * synchronized (s) { * Iterator i = s.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned set will be serializable if the specified set is * serializable. * * @param <T> the class of the objects in the set * @param s the set to be "wrapped" in a synchronized set. * @return a synchronized view of the specified set. */ public static <T> Set<T> synchronizedSet(Set<T> s) { return new SynchronizedSet<>(s); } static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) { return new SynchronizedSet<>(s, mutex); } /** * @serial include */ static class SynchronizedSet<E> extends SynchronizedCollection<E> implements Set<E> { private static final long serialVersionUID = 487447009682186044L; SynchronizedSet(Set<E> s) { super(s); } SynchronizedSet(Set<E> s, Object mutex) { super(s, mutex); } public boolean equals(Object o) { if (this == o) return true; synchronized (mutex) { return c.equals(o); } } public int hashCode() { synchronized (mutex) { return c.hashCode(); } } } /** * Returns a synchronized (thread-safe) sorted set backed by the specified * sorted set. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing sorted set is accomplished * through the returned sorted set (or its views).<p> * * It is imperative that the user manually synchronize on the returned * sorted set when traversing it or any of its {@code subSet}, * {@code headSet}, or {@code tailSet} views via {@link Iterator}, * {@link Spliterator} or {@link Stream}: * <pre> * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); * ... * synchronized (s) { * Iterator i = s.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * or: * <pre> * SortedSet s = Collections.synchronizedSortedSet(new TreeSet()); * SortedSet s2 = s.headSet(foo); * ... * synchronized (s) { // Note: s, not s2!!! * Iterator i = s2.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned sorted set will be serializable if the specified * sorted set is serializable. * * @param <T> the class of the objects in the set * @param s the sorted set to be "wrapped" in a synchronized sorted set. * @return a synchronized view of the specified sorted set. */ public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) { return new SynchronizedSortedSet<>(s); } /** * @serial include */ static class SynchronizedSortedSet<E> extends SynchronizedSet<E> implements SortedSet<E> { private static final long serialVersionUID = 8695801310862127406L; private final SortedSet<E> ss; SynchronizedSortedSet(SortedSet<E> s) { super(s); ss = s; } SynchronizedSortedSet(SortedSet<E> s, Object mutex) { super(s, mutex); ss = s; } public Comparator<? super E> comparator() { synchronized (mutex) { return ss.comparator(); } } public SortedSet<E> subSet(E fromElement, E toElement) { synchronized (mutex) { return new SynchronizedSortedSet<>(ss.subSet(fromElement, toElement), mutex); } } public SortedSet<E> headSet(E toElement) { synchronized (mutex) { return new SynchronizedSortedSet<>(ss.headSet(toElement), mutex); } } public SortedSet<E> tailSet(E fromElement) { synchronized (mutex) { return new SynchronizedSortedSet<>(ss.tailSet(fromElement), mutex); } } public E first() { synchronized (mutex) { return ss.first(); } } public E last() { synchronized (mutex) { return ss.last(); } } } /** * Returns a synchronized (thread-safe) navigable set backed by the * specified navigable set. In order to guarantee serial access, it is * critical that <strong>all</strong> access to the backing navigable set is * accomplished through the returned navigable set (or its views).<p> * * It is imperative that the user manually synchronize on the returned * navigable set when traversing it, or any of its {@code subSet}, * {@code headSet}, or {@code tailSet} views, via {@link Iterator}, * {@link Spliterator} or {@link Stream}: * <pre> * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); * ... * synchronized (s) { * Iterator i = s.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * or: * <pre> * NavigableSet s = Collections.synchronizedNavigableSet(new TreeSet()); * NavigableSet s2 = s.headSet(foo, true); * ... * synchronized (s) { // Note: s, not s2!!! * Iterator i = s2.iterator(); // Must be in the synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned navigable set will be serializable if the specified * navigable set is serializable. * * @param <T> the class of the objects in the set * @param s the navigable set to be "wrapped" in a synchronized navigable * set * @return a synchronized view of the specified navigable set * @since 1.8 */ public static <T> NavigableSet<T> synchronizedNavigableSet(NavigableSet<T> s) { return new SynchronizedNavigableSet<>(s); } /** * @serial include */ static class SynchronizedNavigableSet<E> extends SynchronizedSortedSet<E> implements NavigableSet<E> { private static final long serialVersionUID = -5505529816273629798L; private final NavigableSet<E> ns; SynchronizedNavigableSet(NavigableSet<E> s) { super(s); ns = s; } SynchronizedNavigableSet(NavigableSet<E> s, Object mutex) { super(s, mutex); ns = s; } public E lower(E e) { synchronized (mutex) { return ns.lower(e); } } public E floor(E e) { synchronized (mutex) { return ns.floor(e); } } public E ceiling(E e) { synchronized (mutex) { return ns.ceiling(e); } } public E higher(E e) { synchronized (mutex) { return ns.higher(e); } } public E pollFirst() { synchronized (mutex) { return ns.pollFirst(); } } public E pollLast() { synchronized (mutex) { return ns.pollLast(); } } public NavigableSet<E> descendingSet() { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.descendingSet(), mutex); } } public Iterator<E> descendingIterator() { synchronized (mutex) { return descendingSet().iterator(); } } public NavigableSet<E> subSet(E fromElement, E toElement) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.subSet(fromElement, true, toElement, false), mutex); } } public NavigableSet<E> headSet(E toElement) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.headSet(toElement, false), mutex); } } public NavigableSet<E> tailSet(E fromElement) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, true), mutex); } } public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), mutex); } } public NavigableSet<E> headSet(E toElement, boolean inclusive) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.headSet(toElement, inclusive), mutex); } } public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { synchronized (mutex) { return new SynchronizedNavigableSet<>(ns.tailSet(fromElement, inclusive), mutex); } } } /** * Returns a synchronized (thread-safe) list backed by the specified * list. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing list is accomplished * through the returned list.<p> * * It is imperative that the user manually synchronize on the returned * list when traversing it via {@link Iterator}, {@link Spliterator} * or {@link Stream}: * <pre> * List list = Collections.synchronizedList(new ArrayList()); * ... * synchronized (list) { * Iterator i = list.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned list will be serializable if the specified list is * serializable. * * @param <T> the class of the objects in the list * @param list the list to be "wrapped" in a synchronized list. * @return a synchronized view of the specified list. */ public static <T> List<T> synchronizedList(List<T> list) { return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<>(list) : new SynchronizedList<>(list)); } static <T> List<T> synchronizedList(List<T> list, Object mutex) { return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<>(list, mutex) : new SynchronizedList<>(list, mutex)); } /** * @serial include */ static class SynchronizedList<E> extends SynchronizedCollection<E> implements List<E> { private static final long serialVersionUID = -7754090372962971524L; final List<E> list; SynchronizedList(List<E> list) { super(list); this.list = list; } SynchronizedList(List<E> list, Object mutex) { super(list, mutex); this.list = list; } public boolean equals(Object o) { if (this == o) return true; synchronized (mutex) { return list.equals(o); } } public int hashCode() { synchronized (mutex) { return list.hashCode(); } } public E get(int index) { synchronized (mutex) { return list.get(index); } } public E set(int index, E element) { synchronized (mutex) { return list.set(index, element); } } public void add(int index, E element) { synchronized (mutex) { list.add(index, element); } } public E remove(int index) { synchronized (mutex) { return list.remove(index); } } public int indexOf(Object o) { synchronized (mutex) { return list.indexOf(o); } } public int lastIndexOf(Object o) { synchronized (mutex) { return list.lastIndexOf(o); } } public boolean addAll(int index, Collection<? extends E> c) { synchronized (mutex) { return list.addAll(index, c); } } public ListIterator<E> listIterator() { return list.listIterator(); // Must be manually synched by user } public ListIterator<E> listIterator(int index) { return list.listIterator(index); // Must be manually synched by user } public List<E> subList(int fromIndex, int toIndex) { synchronized (mutex) { return new SynchronizedList<>(list.subList(fromIndex, toIndex), mutex); } } @Override public void replaceAll(UnaryOperator<E> operator) { synchronized (mutex) { list.replaceAll(operator); } } @Override public void sort(Comparator<? super E> c) { synchronized (mutex) { list.sort(c); } } /** * SynchronizedRandomAccessList instances are serialized as * SynchronizedList instances to allow them to be deserialized * in pre-1.4 JREs (which do not have SynchronizedRandomAccessList). * This method inverts the transformation. As a beneficial * side-effect, it also grafts the RandomAccess marker onto * SynchronizedList instances that were serialized in pre-1.4 JREs. * * Note: Unfortunately, SynchronizedRandomAccessList instances * serialized in 1.4.1 and deserialized in 1.4 will become * SynchronizedList instances, as this method was missing in 1.4. */ private Object readResolve() { return (list instanceof RandomAccess ? new SynchronizedRandomAccessList<>(list) : this); } } /** * @serial include */ static class SynchronizedRandomAccessList<E> extends SynchronizedList<E> implements RandomAccess { SynchronizedRandomAccessList(List<E> list) { super(list); } SynchronizedRandomAccessList(List<E> list, Object mutex) { super(list, mutex); } public List<E> subList(int fromIndex, int toIndex) { synchronized (mutex) { return new SynchronizedRandomAccessList<>(list.subList(fromIndex, toIndex), mutex); } } private static final long serialVersionUID = 1530674583602358482L; /** * Allows instances to be deserialized in pre-1.4 JREs (which do * not have SynchronizedRandomAccessList). SynchronizedList has * a readResolve method that inverts this transformation upon * deserialization. */ private Object writeReplace() { return new SynchronizedList<>(list); } } /** * Returns a synchronized (thread-safe) map backed by the specified * map. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing map is accomplished * through the returned map.<p> * * It is imperative that the user manually synchronize on the returned * map when traversing any of its collection views via {@link Iterator}, * {@link Spliterator} or {@link Stream}: * <pre> * Map m = Collections.synchronizedMap(new HashMap()); * ... * Set s = m.keySet(); // Needn't be in synchronized block * ... * synchronized (m) { // Synchronizing on m, not s! * Iterator i = s.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned map will be serializable if the specified map is * serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the map to be "wrapped" in a synchronized map. * @return a synchronized view of the specified map. */ public static <K, V> Map<K, V> synchronizedMap(Map<K, V> m) { return new SynchronizedMap<>(m); } /** * @serial include */ private static class SynchronizedMap<K, V> implements Map<K, V>, Serializable { private static final long serialVersionUID = 1978198479659022715L; private final Map<K, V> m; // Backing Map final Object mutex; // Object on which to synchronize SynchronizedMap(Map<K, V> m) { this.m = Objects.requireNonNull(m); mutex = this; } SynchronizedMap(Map<K, V> m, Object mutex) { this.m = m; this.mutex = mutex; } public int size() { synchronized (mutex) { return m.size(); } } public boolean isEmpty() { synchronized (mutex) { return m.isEmpty(); } } public boolean containsKey(Object key) { synchronized (mutex) { return m.containsKey(key); } } public boolean containsValue(Object value) { synchronized (mutex) { return m.containsValue(value); } } public V get(Object key) { synchronized (mutex) { return m.get(key); } } public V put(K key, V value) { synchronized (mutex) { return m.put(key, value); } } public V remove(Object key) { synchronized (mutex) { return m.remove(key); } } public void putAll(Map<? extends K, ? extends V> map) { synchronized (mutex) { m.putAll(map); } } public void clear() { synchronized (mutex) { m.clear(); } } private transient Set<K> keySet; private transient Set<Map.Entry<K, V>> entrySet; private transient Collection<V> values; public Set<K> keySet() { synchronized (mutex) { if (keySet == null) keySet = new SynchronizedSet<>(m.keySet(), mutex); return keySet; } } public Set<Map.Entry<K, V>> entrySet() { synchronized (mutex) { if (entrySet == null) entrySet = new SynchronizedSet<>(m.entrySet(), mutex); return entrySet; } } public Collection<V> values() { synchronized (mutex) { if (values == null) values = new SynchronizedCollection<>(m.values(), mutex); return values; } } public boolean equals(Object o) { if (this == o) return true; synchronized (mutex) { return m.equals(o); } } public int hashCode() { synchronized (mutex) { return m.hashCode(); } } public String toString() { synchronized (mutex) { return m.toString(); } } // Override default methods in Map @Override public V getOrDefault(Object k, V defaultValue) { synchronized (mutex) { return m.getOrDefault(k, defaultValue); } } @Override public void forEach(BiConsumer<? super K, ? super V> action) { synchronized (mutex) { m.forEach(action); } } @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { synchronized (mutex) { m.replaceAll(function); } } @Override public V putIfAbsent(K key, V value) { synchronized (mutex) { return m.putIfAbsent(key, value); } } @Override public boolean remove(Object key, Object value) { synchronized (mutex) { return m.remove(key, value); } } @Override public boolean replace(K key, V oldValue, V newValue) { synchronized (mutex) { return m.replace(key, oldValue, newValue); } } @Override public V replace(K key, V value) { synchronized (mutex) { return m.replace(key, value); } } @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { synchronized (mutex) { return m.computeIfAbsent(key, mappingFunction); } } @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { synchronized (mutex) { return m.computeIfPresent(key, remappingFunction); } } @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { synchronized (mutex) { return m.compute(key, remappingFunction); } } @Override public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { synchronized (mutex) { return m.merge(key, value, remappingFunction); } } private void writeObject(ObjectOutputStream s) throws IOException { synchronized (mutex) { s.defaultWriteObject(); } } } /** * Returns a synchronized (thread-safe) sorted map backed by the specified * sorted map. In order to guarantee serial access, it is critical that * <strong>all</strong> access to the backing sorted map is accomplished * through the returned sorted map (or its views).<p> * * It is imperative that the user manually synchronize on the returned * sorted map when traversing any of its collection views, or the * collections views of any of its {@code subMap}, {@code headMap} or * {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or * {@link Stream}: * <pre> * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); * ... * Set s = m.keySet(); // Needn't be in synchronized block * ... * synchronized (m) { // Synchronizing on m, not s! * Iterator i = s.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * or: * <pre> * SortedMap m = Collections.synchronizedSortedMap(new TreeMap()); * SortedMap m2 = m.subMap(foo, bar); * ... * Set s2 = m2.keySet(); // Needn't be in synchronized block * ... * synchronized (m) { // Synchronizing on m, not m2 or s2! * Iterator i = s2.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned sorted map will be serializable if the specified * sorted map is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the sorted map to be "wrapped" in a synchronized sorted map. * @return a synchronized view of the specified sorted map. */ public static <K, V> SortedMap<K, V> synchronizedSortedMap(SortedMap<K, V> m) { return new SynchronizedSortedMap<>(m); } /** * @serial include */ static class SynchronizedSortedMap<K, V> extends SynchronizedMap<K, V> implements SortedMap<K, V> { private static final long serialVersionUID = -8798146769416483793L; private final SortedMap<K, V> sm; SynchronizedSortedMap(SortedMap<K, V> m) { super(m); sm = m; } SynchronizedSortedMap(SortedMap<K, V> m, Object mutex) { super(m, mutex); sm = m; } public Comparator<? super K> comparator() { synchronized (mutex) { return sm.comparator(); } } public SortedMap<K, V> subMap(K fromKey, K toKey) { synchronized (mutex) { return new SynchronizedSortedMap<>(sm.subMap(fromKey, toKey), mutex); } } public SortedMap<K, V> headMap(K toKey) { synchronized (mutex) { return new SynchronizedSortedMap<>(sm.headMap(toKey), mutex); } } public SortedMap<K, V> tailMap(K fromKey) { synchronized (mutex) { return new SynchronizedSortedMap<>(sm.tailMap(fromKey), mutex); } } public K firstKey() { synchronized (mutex) { return sm.firstKey(); } } public K lastKey() { synchronized (mutex) { return sm.lastKey(); } } } /** * Returns a synchronized (thread-safe) navigable map backed by the * specified navigable map. In order to guarantee serial access, it is * critical that <strong>all</strong> access to the backing navigable map is * accomplished through the returned navigable map (or its views).<p> * * It is imperative that the user manually synchronize on the returned * navigable map when traversing any of its collection views, or the * collections views of any of its {@code subMap}, {@code headMap} or * {@code tailMap} views, via {@link Iterator}, {@link Spliterator} or * {@link Stream}: * <pre> * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); * ... * Set s = m.keySet(); // Needn't be in synchronized block * ... * synchronized (m) { // Synchronizing on m, not s! * Iterator i = s.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * or: * <pre> * NavigableMap m = Collections.synchronizedNavigableMap(new TreeMap()); * NavigableMap m2 = m.subMap(foo, true, bar, false); * ... * Set s2 = m2.keySet(); // Needn't be in synchronized block * ... * synchronized (m) { // Synchronizing on m, not m2 or s2! * Iterator i = s.iterator(); // Must be in synchronized block * while (i.hasNext()) * foo(i.next()); * } * </pre> * Failure to follow this advice may result in non-deterministic behavior. * * <p>The returned navigable map will be serializable if the specified * navigable map is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the navigable map to be "wrapped" in a synchronized navigable * map * @return a synchronized view of the specified navigable map. * @since 1.8 */ public static <K, V> NavigableMap<K, V> synchronizedNavigableMap(NavigableMap<K, V> m) { return new SynchronizedNavigableMap<>(m); } /** * A synchronized NavigableMap. * * @serial include */ static class SynchronizedNavigableMap<K, V> extends SynchronizedSortedMap<K, V> implements NavigableMap<K, V> { private static final long serialVersionUID = 699392247599746807L; private final NavigableMap<K, V> nm; SynchronizedNavigableMap(NavigableMap<K, V> m) { super(m); nm = m; } SynchronizedNavigableMap(NavigableMap<K, V> m, Object mutex) { super(m, mutex); nm = m; } public Entry<K, V> lowerEntry(K key) { synchronized (mutex) { return nm.lowerEntry(key); } } public K lowerKey(K key) { synchronized (mutex) { return nm.lowerKey(key); } } public Entry<K, V> floorEntry(K key) { synchronized (mutex) { return nm.floorEntry(key); } } public K floorKey(K key) { synchronized (mutex) { return nm.floorKey(key); } } public Entry<K, V> ceilingEntry(K key) { synchronized (mutex) { return nm.ceilingEntry(key); } } public K ceilingKey(K key) { synchronized (mutex) { return nm.ceilingKey(key); } } public Entry<K, V> higherEntry(K key) { synchronized (mutex) { return nm.higherEntry(key); } } public K higherKey(K key) { synchronized (mutex) { return nm.higherKey(key); } } public Entry<K, V> firstEntry() { synchronized (mutex) { return nm.firstEntry(); } } public Entry<K, V> lastEntry() { synchronized (mutex) { return nm.lastEntry(); } } public Entry<K, V> pollFirstEntry() { synchronized (mutex) { return nm.pollFirstEntry(); } } public Entry<K, V> pollLastEntry() { synchronized (mutex) { return nm.pollLastEntry(); } } public NavigableMap<K, V> descendingMap() { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.descendingMap(), mutex); } } public NavigableSet<K> keySet() { return navigableKeySet(); } public NavigableSet<K> navigableKeySet() { synchronized (mutex) { return new SynchronizedNavigableSet<>(nm.navigableKeySet(), mutex); } } public NavigableSet<K> descendingKeySet() { synchronized (mutex) { return new SynchronizedNavigableSet<>(nm.descendingKeySet(), mutex); } } public SortedMap<K, V> subMap(K fromKey, K toKey) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.subMap(fromKey, true, toKey, false), mutex); } } public SortedMap<K, V> headMap(K toKey) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.headMap(toKey, false), mutex); } } public SortedMap<K, V> tailMap(K fromKey) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, true), mutex); } } public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), mutex); } } public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.headMap(toKey, inclusive), mutex); } } public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { synchronized (mutex) { return new SynchronizedNavigableMap<>(nm.tailMap(fromKey, inclusive), mutex); } } } // Dynamically typesafe collection wrappers /** * Returns a dynamically typesafe view of the specified collection. * Any attempt to insert an element of the wrong type will result in an * immediate {@link ClassCastException}. Assuming a collection * contains no incorrectly typed elements prior to the time a * dynamically typesafe view is generated, and that all subsequent * access to the collection takes place through the view, it is * <i>guaranteed</i> that the collection cannot contain an incorrectly * typed element. * * <p>The generics mechanism in the language provides compile-time * (static) type checking, but it is possible to defeat this mechanism * with unchecked casts. Usually this is not a problem, as the compiler * issues warnings on all such unchecked operations. There are, however, * times when static type checking alone is not sufficient. For example, * suppose a collection is passed to a third-party library and it is * imperative that the library code not corrupt the collection by * inserting an element of the wrong type. * * <p>Another use of dynamically typesafe views is debugging. Suppose a * program fails with a {@code ClassCastException}, indicating that an * incorrectly typed element was put into a parameterized collection. * Unfortunately, the exception can occur at any time after the erroneous * element is inserted, so it typically provides little or no information * as to the real source of the problem. If the problem is reproducible, * one can quickly determine its source by temporarily modifying the * program to wrap the collection with a dynamically typesafe view. * For example, this declaration: * <pre> {@code * Collection<String> c = new HashSet<>(); * }</pre> * may be replaced temporarily by this one: * <pre> {@code * Collection<String> c = Collections.checkedCollection( * new HashSet<>(), String.class); * }</pre> * Running the program again will cause it to fail at the point where * an incorrectly typed element is inserted into the collection, clearly * identifying the source of the problem. Once the problem is fixed, the * modified declaration may be reverted back to the original. * * <p>The returned collection does <i>not</i> pass the hashCode and equals * operations through to the backing collection, but relies on * {@code Object}'s {@code equals} and {@code hashCode} methods. This * is necessary to preserve the contracts of these operations in the case * that the backing collection is a set or a list. * * <p>The returned collection will be serializable if the specified * collection is serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned collection permits insertion of null elements * whenever the backing collection does. * * @param <E> the class of the objects in the collection * @param c the collection for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code c} is permitted to hold * @return a dynamically typesafe view of the specified collection * @since 1.5 */ public static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type) { return new CheckedCollection<>(c, type); } @SuppressWarnings("unchecked") static <T> T[] zeroLengthArray(Class<T> type) { return (T[]) Array.newInstance(type, 0); } /** * @serial include */ static class CheckedCollection<E> implements Collection<E>, Serializable { private static final long serialVersionUID = 1578914078182001775L; final Collection<E> c; final Class<E> type; @SuppressWarnings("unchecked") E typeCheck(Object o) { if (o != null && !type.isInstance(o)) throw new ClassCastException(badElementMsg(o)); return (E) o; } private String badElementMsg(Object o) { return "Attempt to insert " + o.getClass() + " element into collection with element type " + type; } CheckedCollection(Collection<E> c, Class<E> type) { this.c = Objects.requireNonNull(c, "c"); this.type = Objects.requireNonNull(type, "type"); } public int size() { return c.size(); } public boolean isEmpty() { return c.isEmpty(); } public boolean contains(Object o) { return c.contains(o); } public Object[] toArray() { return c.toArray(); } public <T> T[] toArray(T[] a) { return c.toArray(a); } public <T> T[] toArray(IntFunction<T[]> f) { return c.toArray(f); } public String toString() { return c.toString(); } public boolean remove(Object o) { return c.remove(o); } public void clear() { c.clear(); } public boolean containsAll(Collection<?> coll) { return c.containsAll(coll); } public boolean removeAll(Collection<?> coll) { return c.removeAll(coll); } public boolean retainAll(Collection<?> coll) { return c.retainAll(coll); } public Iterator<E> iterator() { // JDK-6363904 - unwrapped iterator could be typecast to // ListIterator with unsafe set() final Iterator<E> it = c.iterator(); return new Iterator<E>() { public boolean hasNext() { return it.hasNext(); } public E next() { return it.next(); } public void remove() { it.remove(); } public void forEachRemaining(Consumer<? super E> action) { it.forEachRemaining(action); } }; } public boolean add(E e) { return c.add(typeCheck(e)); } private E[] zeroLengthElementArray; // Lazily initialized private E[] zeroLengthElementArray() { return zeroLengthElementArray != null ? zeroLengthElementArray : (zeroLengthElementArray = zeroLengthArray(type)); } @SuppressWarnings("unchecked") Collection<E> checkedCopyOf(Collection<? extends E> coll) { Object[] a; try { E[] z = zeroLengthElementArray(); a = coll.toArray(z); // Defend against coll violating the toArray contract if (a.getClass() != z.getClass()) a = Arrays.copyOf(a, a.length, z.getClass()); } catch (ArrayStoreException ignore) { // To get better and consistent diagnostics, // we call typeCheck explicitly on each element. // We call clone() to defend against coll retaining a // reference to the returned array and storing a bad // element into it after it has been type checked. a = coll.toArray().clone(); for (Object o : a) typeCheck(o); } // A slight abuse of the type system, but safe here. return (Collection<E>) Arrays.asList(a); } public boolean addAll(Collection<? extends E> coll) { // Doing things this way insulates us from concurrent changes // in the contents of coll and provides all-or-nothing // semantics (which we wouldn't get if we type-checked each // element as we added it) return c.addAll(checkedCopyOf(coll)); } // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { c.forEach(action); } @Override public boolean removeIf(Predicate<? super E> filter) { return c.removeIf(filter); } @Override public Spliterator<E> spliterator() { return c.spliterator(); } @Override public Stream<E> stream() { return c.stream(); } @Override public Stream<E> parallelStream() { return c.parallelStream(); } } /** * Returns a dynamically typesafe view of the specified queue. * Any attempt to insert an element of the wrong type will result in * an immediate {@link ClassCastException}. Assuming a queue contains * no incorrectly typed elements prior to the time a dynamically typesafe * view is generated, and that all subsequent access to the queue * takes place through the view, it is <i>guaranteed</i> that the * queue cannot contain an incorrectly typed element. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned queue will be serializable if the specified queue * is serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned queue permits insertion of {@code null} elements * whenever the backing queue does. * * @param <E> the class of the objects in the queue * @param queue the queue for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code queue} is permitted to hold * @return a dynamically typesafe view of the specified queue * @since 1.8 */ public static <E> Queue<E> checkedQueue(Queue<E> queue, Class<E> type) { return new CheckedQueue<>(queue, type); } /** * @serial include */ static class CheckedQueue<E> extends CheckedCollection<E> implements Queue<E>, Serializable { private static final long serialVersionUID = 1433151992604707767L; final Queue<E> queue; CheckedQueue(Queue<E> queue, Class<E> elementType) { super(queue, elementType); this.queue = queue; } public E element() { return queue.element(); } public boolean equals(Object o) { return o == this || c.equals(o); } public int hashCode() { return c.hashCode(); } public E peek() { return queue.peek(); } public E poll() { return queue.poll(); } public E remove() { return queue.remove(); } public boolean offer(E e) { return queue.offer(typeCheck(e)); } } /** * Returns a dynamically typesafe view of the specified set. * Any attempt to insert an element of the wrong type will result in * an immediate {@link ClassCastException}. Assuming a set contains * no incorrectly typed elements prior to the time a dynamically typesafe * view is generated, and that all subsequent access to the set * takes place through the view, it is <i>guaranteed</i> that the * set cannot contain an incorrectly typed element. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned set will be serializable if the specified set is * serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned set permits insertion of null elements whenever * the backing set does. * * @param <E> the class of the objects in the set * @param s the set for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code s} is permitted to hold * @return a dynamically typesafe view of the specified set * @since 1.5 */ public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) { return new CheckedSet<>(s, type); } /** * @serial include */ static class CheckedSet<E> extends CheckedCollection<E> implements Set<E>, Serializable { private static final long serialVersionUID = 4694047833775013803L; CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); } public boolean equals(Object o) { return o == this || c.equals(o); } public int hashCode() { return c.hashCode(); } } /** * Returns a dynamically typesafe view of the specified sorted set. * Any attempt to insert an element of the wrong type will result in an * immediate {@link ClassCastException}. Assuming a sorted set * contains no incorrectly typed elements prior to the time a * dynamically typesafe view is generated, and that all subsequent * access to the sorted set takes place through the view, it is * <i>guaranteed</i> that the sorted set cannot contain an incorrectly * typed element. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned sorted set will be serializable if the specified sorted * set is serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned sorted set permits insertion of null elements * whenever the backing sorted set does. * * @param <E> the class of the objects in the set * @param s the sorted set for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code s} is permitted to hold * @return a dynamically typesafe view of the specified sorted set * @since 1.5 */ public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s, Class<E> type) { return new CheckedSortedSet<>(s, type); } /** * @serial include */ static class CheckedSortedSet<E> extends CheckedSet<E> implements SortedSet<E>, Serializable { private static final long serialVersionUID = 1599911165492914959L; private final SortedSet<E> ss; CheckedSortedSet(SortedSet<E> s, Class<E> type) { super(s, type); ss = s; } public Comparator<? super E> comparator() { return ss.comparator(); } public E first() { return ss.first(); } public E last() { return ss.last(); } public SortedSet<E> subSet(E fromElement, E toElement) { return checkedSortedSet(ss.subSet(fromElement, toElement), type); } public SortedSet<E> headSet(E toElement) { return checkedSortedSet(ss.headSet(toElement), type); } public SortedSet<E> tailSet(E fromElement) { return checkedSortedSet(ss.tailSet(fromElement), type); } } /** * Returns a dynamically typesafe view of the specified navigable set. * Any attempt to insert an element of the wrong type will result in an * immediate {@link ClassCastException}. Assuming a navigable set * contains no incorrectly typed elements prior to the time a * dynamically typesafe view is generated, and that all subsequent * access to the navigable set takes place through the view, it is * <em>guaranteed</em> that the navigable set cannot contain an incorrectly * typed element. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned navigable set will be serializable if the specified * navigable set is serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned navigable set permits insertion of null elements * whenever the backing sorted set does. * * @param <E> the class of the objects in the set * @param s the navigable set for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code s} is permitted to hold * @return a dynamically typesafe view of the specified navigable set * @since 1.8 */ public static <E> NavigableSet<E> checkedNavigableSet(NavigableSet<E> s, Class<E> type) { return new CheckedNavigableSet<>(s, type); } /** * @serial include */ static class CheckedNavigableSet<E> extends CheckedSortedSet<E> implements NavigableSet<E>, Serializable { private static final long serialVersionUID = -5429120189805438922L; private final NavigableSet<E> ns; CheckedNavigableSet(NavigableSet<E> s, Class<E> type) { super(s, type); ns = s; } public E lower(E e) { return ns.lower(e); } public E floor(E e) { return ns.floor(e); } public E ceiling(E e) { return ns.ceiling(e); } public E higher(E e) { return ns.higher(e); } public E pollFirst() { return ns.pollFirst(); } public E pollLast() { return ns.pollLast(); } public NavigableSet<E> descendingSet() { return checkedNavigableSet(ns.descendingSet(), type); } public Iterator<E> descendingIterator() { return checkedNavigableSet(ns.descendingSet(), type).iterator(); } public NavigableSet<E> subSet(E fromElement, E toElement) { return checkedNavigableSet(ns.subSet(fromElement, true, toElement, false), type); } public NavigableSet<E> headSet(E toElement) { return checkedNavigableSet(ns.headSet(toElement, false), type); } public NavigableSet<E> tailSet(E fromElement) { return checkedNavigableSet(ns.tailSet(fromElement, true), type); } public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return checkedNavigableSet(ns.subSet(fromElement, fromInclusive, toElement, toInclusive), type); } public NavigableSet<E> headSet(E toElement, boolean inclusive) { return checkedNavigableSet(ns.headSet(toElement, inclusive), type); } public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { return checkedNavigableSet(ns.tailSet(fromElement, inclusive), type); } } /** * Returns a dynamically typesafe view of the specified list. * Any attempt to insert an element of the wrong type will result in * an immediate {@link ClassCastException}. Assuming a list contains * no incorrectly typed elements prior to the time a dynamically typesafe * view is generated, and that all subsequent access to the list * takes place through the view, it is <i>guaranteed</i> that the * list cannot contain an incorrectly typed element. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned list will be serializable if the specified list * is serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned list permits insertion of null elements whenever * the backing list does. * * @param <E> the class of the objects in the list * @param list the list for which a dynamically typesafe view is to be * returned * @param type the type of element that {@code list} is permitted to hold * @return a dynamically typesafe view of the specified list * @since 1.5 */ public static <E> List<E> checkedList(List<E> list, Class<E> type) { return (list instanceof RandomAccess ? new CheckedRandomAccessList<>(list, type) : new CheckedList<>(list, type)); } /** * @serial include */ static class CheckedList<E> extends CheckedCollection<E> implements List<E> { private static final long serialVersionUID = 65247728283967356L; final List<E> list; CheckedList(List<E> list, Class<E> type) { super(list, type); this.list = list; } public boolean equals(Object o) { return o == this || list.equals(o); } public int hashCode() { return list.hashCode(); } public E get(int index) { return list.get(index); } public E remove(int index) { return list.remove(index); } public int indexOf(Object o) { return list.indexOf(o); } public int lastIndexOf(Object o) { return list.lastIndexOf(o); } public E set(int index, E element) { return list.set(index, typeCheck(element)); } public void add(int index, E element) { list.add(index, typeCheck(element)); } public boolean addAll(int index, Collection<? extends E> c) { return list.addAll(index, checkedCopyOf(c)); } public ListIterator<E> listIterator() { return listIterator(0); } public ListIterator<E> listIterator(final int index) { final ListIterator<E> i = list.listIterator(index); return new ListIterator<E>() { public boolean hasNext() { return i.hasNext(); } public E next() { return i.next(); } public boolean hasPrevious() { return i.hasPrevious(); } public E previous() { return i.previous(); } public int nextIndex() { return i.nextIndex(); } public int previousIndex() { return i.previousIndex(); } public void remove() { i.remove(); } public void set(E e) { i.set(typeCheck(e)); } public void add(E e) { i.add(typeCheck(e)); } @Override public void forEachRemaining(Consumer<? super E> action) { i.forEachRemaining(action); } }; } public List<E> subList(int fromIndex, int toIndex) { return new CheckedList<>(list.subList(fromIndex, toIndex), type); } /** * {@inheritDoc} * * @throws ClassCastException if the class of an element returned by the * operator prevents it from being added to this collection. The * exception may be thrown after some elements of the list have * already been replaced. */ @Override public void replaceAll(UnaryOperator<E> operator) { Objects.requireNonNull(operator); list.replaceAll(e -> typeCheck(operator.apply(e))); } @Override public void sort(Comparator<? super E> c) { list.sort(c); } } /** * @serial include */ static class CheckedRandomAccessList<E> extends CheckedList<E> implements RandomAccess { private static final long serialVersionUID = 1638200125423088369L; CheckedRandomAccessList(List<E> list, Class<E> type) { super(list, type); } public List<E> subList(int fromIndex, int toIndex) { return new CheckedRandomAccessList<>(list.subList(fromIndex, toIndex), type); } } /** * Returns a dynamically typesafe view of the specified map. * Any attempt to insert a mapping whose key or value have the wrong * type will result in an immediate {@link ClassCastException}. * Similarly, any attempt to modify the value currently associated with * a key will result in an immediate {@link ClassCastException}, * whether the modification is attempted directly through the map * itself, or through a {@link Map.Entry} instance obtained from the * map's {@link Map#entrySet() entry set} view. * * <p>Assuming a map contains no incorrectly typed keys or values * prior to the time a dynamically typesafe view is generated, and * that all subsequent access to the map takes place through the view * (or one of its collection views), it is <i>guaranteed</i> that the * map cannot contain an incorrectly typed key or value. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned map will be serializable if the specified map is * serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned map permits insertion of null keys or values * whenever the backing map does. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the map for which a dynamically typesafe view is to be * returned * @param keyType the type of key that {@code m} is permitted to hold * @param valueType the type of value that {@code m} is permitted to hold * @return a dynamically typesafe view of the specified map * @since 1.5 */ public static <K, V> Map<K, V> checkedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { return new CheckedMap<>(m, keyType, valueType); } /** * @serial include */ private static class CheckedMap<K, V> implements Map<K, V>, Serializable { private static final long serialVersionUID = 5742860141034234728L; private final Map<K, V> m; final Class<K> keyType; final Class<V> valueType; private void typeCheck(Object key, Object value) { if (key != null && !keyType.isInstance(key)) throw new ClassCastException(badKeyMsg(key)); if (value != null && !valueType.isInstance(value)) throw new ClassCastException(badValueMsg(value)); } private BiFunction<? super K, ? super V, ? extends V> typeCheck( BiFunction<? super K, ? super V, ? extends V> func) { Objects.requireNonNull(func); return (k, v) -> { V newValue = func.apply(k, v); typeCheck(k, newValue); return newValue; }; } private String badKeyMsg(Object key) { return "Attempt to insert " + key.getClass() + " key into map with key type " + keyType; } private String badValueMsg(Object value) { return "Attempt to insert " + value.getClass() + " value into map with value type " + valueType; } CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) { this.m = Objects.requireNonNull(m); this.keyType = Objects.requireNonNull(keyType); this.valueType = Objects.requireNonNull(valueType); } public int size() { return m.size(); } public boolean isEmpty() { return m.isEmpty(); } public boolean containsKey(Object key) { return m.containsKey(key); } public boolean containsValue(Object v) { return m.containsValue(v); } public V get(Object key) { return m.get(key); } public V remove(Object key) { return m.remove(key); } public void clear() { m.clear(); } public Set<K> keySet() { return m.keySet(); } public Collection<V> values() { return m.values(); } public boolean equals(Object o) { return o == this || m.equals(o); } public int hashCode() { return m.hashCode(); } public String toString() { return m.toString(); } public V put(K key, V value) { typeCheck(key, value); return m.put(key, value); } @SuppressWarnings("unchecked") public void putAll(Map<? extends K, ? extends V> t) { // Satisfy the following goals: // - good diagnostics in case of type mismatch // - all-or-nothing semantics // - protection from malicious t // - correct behavior if t is a concurrent map Object[] entries = t.entrySet().toArray(); List<Map.Entry<K, V>> checked = new ArrayList<>(entries.length); for (Object o : entries) { Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; Object k = e.getKey(); Object v = e.getValue(); typeCheck(k, v); checked.add(new AbstractMap.SimpleImmutableEntry<>((K) k, (V) v)); } for (Map.Entry<K, V> e : checked) m.put(e.getKey(), e.getValue()); } private transient Set<Map.Entry<K, V>> entrySet; public Set<Map.Entry<K, V>> entrySet() { if (entrySet == null) entrySet = new CheckedEntrySet<>(m.entrySet(), valueType); return entrySet; } // Override default methods in Map @Override public void forEach(BiConsumer<? super K, ? super V> action) { m.forEach(action); } @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { m.replaceAll(typeCheck(function)); } @Override public V putIfAbsent(K key, V value) { typeCheck(key, value); return m.putIfAbsent(key, value); } @Override public boolean remove(Object key, Object value) { return m.remove(key, value); } @Override public boolean replace(K key, V oldValue, V newValue) { typeCheck(key, newValue); return m.replace(key, oldValue, newValue); } @Override public V replace(K key, V value) { typeCheck(key, value); return m.replace(key, value); } @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { Objects.requireNonNull(mappingFunction); return m.computeIfAbsent(key, k -> { V value = mappingFunction.apply(k); typeCheck(k, value); return value; }); } @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { return m.computeIfPresent(key, typeCheck(remappingFunction)); } @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { return m.compute(key, typeCheck(remappingFunction)); } @Override public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { Objects.requireNonNull(remappingFunction); return m.merge(key, value, (v1, v2) -> { V newValue = remappingFunction.apply(v1, v2); typeCheck(null, newValue); return newValue; }); } /** * We need this class in addition to CheckedSet as Map.Entry permits * modification of the backing Map via the setValue operation. This * class is subtle: there are many possible attacks that must be * thwarted. * * @serial exclude */ static class CheckedEntrySet<K, V> implements Set<Map.Entry<K, V>> { private final Set<Map.Entry<K, V>> s; private final Class<V> valueType; CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) { this.s = s; this.valueType = valueType; } public int size() { return s.size(); } public boolean isEmpty() { return s.isEmpty(); } public String toString() { return s.toString(); } public int hashCode() { return s.hashCode(); } public void clear() { s.clear(); } public boolean add(Map.Entry<K, V> e) { throw new UnsupportedOperationException(); } public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) { throw new UnsupportedOperationException(); } public Iterator<Map.Entry<K, V>> iterator() { final Iterator<Map.Entry<K, V>> i = s.iterator(); return new Iterator<Map.Entry<K, V>>() { public boolean hasNext() { return i.hasNext(); } public void remove() { i.remove(); } public Map.Entry<K, V> next() { return checkedEntry(i.next(), valueType); } public void forEachRemaining(Consumer<? super Entry<K, V>> action) { i.forEachRemaining(e -> action.accept(checkedEntry(e, valueType))); } }; } @SuppressWarnings("unchecked") public Object[] toArray() { Object[] source = s.toArray(); /* * Ensure that we don't get an ArrayStoreException even if * s.toArray returns an array of something other than Object */ Object[] dest = (source.getClass() == Object[].class) ? source : new Object[source.length]; for (int i = 0; i < source.length; i++) dest[i] = checkedEntry((Map.Entry<K, V>) source[i], valueType); return dest; } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { // We don't pass a to s.toArray, to avoid window of // vulnerability wherein an unscrupulous multithreaded client // could get his hands on raw (unwrapped) Entries from s. T[] arr = s.toArray(a.length == 0 ? a : Arrays.copyOf(a, 0)); for (int i = 0; i < arr.length; i++) arr[i] = (T) checkedEntry((Map.Entry<K, V>) arr[i], valueType); if (arr.length > a.length) return arr; System.arraycopy(arr, 0, a, 0, arr.length); if (a.length > arr.length) a[arr.length] = null; return a; } /** * This method is overridden to protect the backing set against * an object with a nefarious equals function that senses * that the equality-candidate is Map.Entry and calls its * setValue method. */ public boolean contains(Object o) { if (!(o instanceof Map.Entry)) return false; Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; return s.contains((e instanceof CheckedEntry) ? e : checkedEntry(e, valueType)); } /** * The bulk collection methods are overridden to protect * against an unscrupulous collection whose contains(Object o) * method senses when o is a Map.Entry, and calls o.setValue. */ public boolean containsAll(Collection<?> c) { for (Object o : c) if (!contains(o)) // Invokes safe contains() above return false; return true; } public boolean remove(Object o) { if (!(o instanceof Map.Entry)) return false; return s.remove(new AbstractMap.SimpleImmutableEntry<>((Map.Entry<?, ?>) o)); } public boolean removeAll(Collection<?> c) { return batchRemove(c, false); } public boolean retainAll(Collection<?> c) { return batchRemove(c, true); } private boolean batchRemove(Collection<?> c, boolean complement) { Objects.requireNonNull(c); boolean modified = false; Iterator<Map.Entry<K, V>> it = iterator(); while (it.hasNext()) { if (c.contains(it.next()) != complement) { it.remove(); modified = true; } } return modified; } public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof Set)) return false; Set<?> that = (Set<?>) o; return that.size() == s.size() && containsAll(that); // Invokes safe containsAll() above } static <K, V, T> CheckedEntry<K, V, T> checkedEntry(Map.Entry<K, V> e, Class<T> valueType) { return new CheckedEntry<>(e, valueType); } /** * This "wrapper class" serves two purposes: it prevents * the client from modifying the backing Map, by short-circuiting * the setValue method, and it protects the backing Map against * an ill-behaved Map.Entry that attempts to modify another * Map.Entry when asked to perform an equality check. */ private static class CheckedEntry<K, V, T> implements Map.Entry<K, V> { private final Map.Entry<K, V> e; private final Class<T> valueType; CheckedEntry(Map.Entry<K, V> e, Class<T> valueType) { this.e = Objects.requireNonNull(e); this.valueType = Objects.requireNonNull(valueType); } public K getKey() { return e.getKey(); } public V getValue() { return e.getValue(); } public int hashCode() { return e.hashCode(); } public String toString() { return e.toString(); } public V setValue(V value) { if (value != null && !valueType.isInstance(value)) throw new ClassCastException(badValueMsg(value)); return e.setValue(value); } private String badValueMsg(Object value) { return "Attempt to insert " + value.getClass() + " value into map with value type " + valueType; } public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof Map.Entry)) return false; return e.equals(new AbstractMap.SimpleImmutableEntry<>((Map.Entry<?, ?>) o)); } } } } /** * Returns a dynamically typesafe view of the specified sorted map. * Any attempt to insert a mapping whose key or value have the wrong * type will result in an immediate {@link ClassCastException}. * Similarly, any attempt to modify the value currently associated with * a key will result in an immediate {@link ClassCastException}, * whether the modification is attempted directly through the map * itself, or through a {@link Map.Entry} instance obtained from the * map's {@link Map#entrySet() entry set} view. * * <p>Assuming a map contains no incorrectly typed keys or values * prior to the time a dynamically typesafe view is generated, and * that all subsequent access to the map takes place through the view * (or one of its collection views), it is <i>guaranteed</i> that the * map cannot contain an incorrectly typed key or value. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned map will be serializable if the specified map is * serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned map permits insertion of null keys or values * whenever the backing map does. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param m the map for which a dynamically typesafe view is to be * returned * @param keyType the type of key that {@code m} is permitted to hold * @param valueType the type of value that {@code m} is permitted to hold * @return a dynamically typesafe view of the specified map * @since 1.5 */ public static <K, V> SortedMap<K, V> checkedSortedMap(SortedMap<K, V> m, Class<K> keyType, Class<V> valueType) { return new CheckedSortedMap<>(m, keyType, valueType); } /** * @serial include */ static class CheckedSortedMap<K, V> extends CheckedMap<K, V> implements SortedMap<K, V>, Serializable { private static final long serialVersionUID = 1599671320688067438L; private final SortedMap<K, V> sm; CheckedSortedMap(SortedMap<K, V> m, Class<K> keyType, Class<V> valueType) { super(m, keyType, valueType); sm = m; } public Comparator<? super K> comparator() { return sm.comparator(); } public K firstKey() { return sm.firstKey(); } public K lastKey() { return sm.lastKey(); } public SortedMap<K, V> subMap(K fromKey, K toKey) { return checkedSortedMap(sm.subMap(fromKey, toKey), keyType, valueType); } public SortedMap<K, V> headMap(K toKey) { return checkedSortedMap(sm.headMap(toKey), keyType, valueType); } public SortedMap<K, V> tailMap(K fromKey) { return checkedSortedMap(sm.tailMap(fromKey), keyType, valueType); } } /** * Returns a dynamically typesafe view of the specified navigable map. * Any attempt to insert a mapping whose key or value have the wrong * type will result in an immediate {@link ClassCastException}. * Similarly, any attempt to modify the value currently associated with * a key will result in an immediate {@link ClassCastException}, * whether the modification is attempted directly through the map * itself, or through a {@link Map.Entry} instance obtained from the * map's {@link Map#entrySet() entry set} view. * * <p>Assuming a map contains no incorrectly typed keys or values * prior to the time a dynamically typesafe view is generated, and * that all subsequent access to the map takes place through the view * (or one of its collection views), it is <em>guaranteed</em> that the * map cannot contain an incorrectly typed key or value. * * <p>A discussion of the use of dynamically typesafe views may be * found in the documentation for the {@link #checkedCollection * checkedCollection} method. * * <p>The returned map will be serializable if the specified map is * serializable. * * <p>Since {@code null} is considered to be a value of any reference * type, the returned map permits insertion of null keys or values * whenever the backing map does. * * @param <K> type of map keys * @param <V> type of map values * @param m the map for which a dynamically typesafe view is to be * returned * @param keyType the type of key that {@code m} is permitted to hold * @param valueType the type of value that {@code m} is permitted to hold * @return a dynamically typesafe view of the specified map * @since 1.8 */ public static <K, V> NavigableMap<K, V> checkedNavigableMap(NavigableMap<K, V> m, Class<K> keyType, Class<V> valueType) { return new CheckedNavigableMap<>(m, keyType, valueType); } /** * @serial include */ static class CheckedNavigableMap<K, V> extends CheckedSortedMap<K, V> implements NavigableMap<K, V>, Serializable { private static final long serialVersionUID = -4852462692372534096L; private final NavigableMap<K, V> nm; CheckedNavigableMap(NavigableMap<K, V> m, Class<K> keyType, Class<V> valueType) { super(m, keyType, valueType); nm = m; } public Comparator<? super K> comparator() { return nm.comparator(); } public K firstKey() { return nm.firstKey(); } public K lastKey() { return nm.lastKey(); } public Entry<K, V> lowerEntry(K key) { Entry<K, V> lower = nm.lowerEntry(key); return (null != lower) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(lower, valueType) : null; } public K lowerKey(K key) { return nm.lowerKey(key); } public Entry<K, V> floorEntry(K key) { Entry<K, V> floor = nm.floorEntry(key); return (null != floor) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(floor, valueType) : null; } public K floorKey(K key) { return nm.floorKey(key); } public Entry<K, V> ceilingEntry(K key) { Entry<K, V> ceiling = nm.ceilingEntry(key); return (null != ceiling) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(ceiling, valueType) : null; } public K ceilingKey(K key) { return nm.ceilingKey(key); } public Entry<K, V> higherEntry(K key) { Entry<K, V> higher = nm.higherEntry(key); return (null != higher) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(higher, valueType) : null; } public K higherKey(K key) { return nm.higherKey(key); } public Entry<K, V> firstEntry() { Entry<K, V> first = nm.firstEntry(); return (null != first) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(first, valueType) : null; } public Entry<K, V> lastEntry() { Entry<K, V> last = nm.lastEntry(); return (null != last) ? new CheckedMap.CheckedEntrySet.CheckedEntry<>(last, valueType) : null; } public Entry<K, V> pollFirstEntry() { Entry<K, V> entry = nm.pollFirstEntry(); return (null == entry) ? null : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); } public Entry<K, V> pollLastEntry() { Entry<K, V> entry = nm.pollLastEntry(); return (null == entry) ? null : new CheckedMap.CheckedEntrySet.CheckedEntry<>(entry, valueType); } public NavigableMap<K, V> descendingMap() { return checkedNavigableMap(nm.descendingMap(), keyType, valueType); } public NavigableSet<K> keySet() { return navigableKeySet(); } public NavigableSet<K> navigableKeySet() { return checkedNavigableSet(nm.navigableKeySet(), keyType); } public NavigableSet<K> descendingKeySet() { return checkedNavigableSet(nm.descendingKeySet(), keyType); } @Override public NavigableMap<K, V> subMap(K fromKey, K toKey) { return checkedNavigableMap(nm.subMap(fromKey, true, toKey, false), keyType, valueType); } @Override public NavigableMap<K, V> headMap(K toKey) { return checkedNavigableMap(nm.headMap(toKey, false), keyType, valueType); } @Override public NavigableMap<K, V> tailMap(K fromKey) { return checkedNavigableMap(nm.tailMap(fromKey, true), keyType, valueType); } public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) { return checkedNavigableMap(nm.subMap(fromKey, fromInclusive, toKey, toInclusive), keyType, valueType); } public NavigableMap<K, V> headMap(K toKey, boolean inclusive) { return checkedNavigableMap(nm.headMap(toKey, inclusive), keyType, valueType); } public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) { return checkedNavigableMap(nm.tailMap(fromKey, inclusive), keyType, valueType); } } // Empty collections /** * Returns an iterator that has no elements. More precisely, * * <ul> * <li>{@link Iterator#hasNext hasNext} always returns {@code * false}.</li> * <li>{@link Iterator#next next} always throws {@link * NoSuchElementException}.</li> * <li>{@link Iterator#remove remove} always throws {@link * IllegalStateException}.</li> * </ul> * * <p>Implementations of this method are permitted, but not * required, to return the same object from multiple invocations. * * @param <T> type of elements, if there were any, in the iterator * @return an empty iterator * @since 1.7 */ @SuppressWarnings("unchecked") public static <T> Iterator<T> emptyIterator() { return (Iterator<T>) EmptyIterator.EMPTY_ITERATOR; } private static class EmptyIterator<E> implements Iterator<E> { static final EmptyIterator<Object> EMPTY_ITERATOR = new EmptyIterator<>(); public boolean hasNext() { return false; } public E next() { throw new NoSuchElementException(); } public void remove() { throw new IllegalStateException(); } @Override public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); } } /** * Returns a list iterator that has no elements. More precisely, * * <ul> * <li>{@link Iterator#hasNext hasNext} and {@link * ListIterator#hasPrevious hasPrevious} always return {@code * false}.</li> * <li>{@link Iterator#next next} and {@link ListIterator#previous * previous} always throw {@link NoSuchElementException}.</li> * <li>{@link Iterator#remove remove} and {@link ListIterator#set * set} always throw {@link IllegalStateException}.</li> * <li>{@link ListIterator#add add} always throws {@link * UnsupportedOperationException}.</li> * <li>{@link ListIterator#nextIndex nextIndex} always returns * {@code 0}.</li> * <li>{@link ListIterator#previousIndex previousIndex} always * returns {@code -1}.</li> * </ul> * * <p>Implementations of this method are permitted, but not * required, to return the same object from multiple invocations. * * @param <T> type of elements, if there were any, in the iterator * @return an empty list iterator * @since 1.7 */ @SuppressWarnings("unchecked") public static <T> ListIterator<T> emptyListIterator() { return (ListIterator<T>) EmptyListIterator.EMPTY_ITERATOR; } private static class EmptyListIterator<E> extends EmptyIterator<E> implements ListIterator<E> { static final EmptyListIterator<Object> EMPTY_ITERATOR = new EmptyListIterator<>(); public boolean hasPrevious() { return false; } public E previous() { throw new NoSuchElementException(); } public int nextIndex() { return 0; } public int previousIndex() { return -1; } public void set(E e) { throw new IllegalStateException(); } public void add(E e) { throw new UnsupportedOperationException(); } } /** * Returns an enumeration that has no elements. More precisely, * * <ul> * <li>{@link Enumeration#hasMoreElements hasMoreElements} always * returns {@code false}.</li> * <li> {@link Enumeration#nextElement nextElement} always throws * {@link NoSuchElementException}.</li> * </ul> * * <p>Implementations of this method are permitted, but not * required, to return the same object from multiple invocations. * * @param <T> the class of the objects in the enumeration * @return an empty enumeration * @since 1.7 */ @SuppressWarnings("unchecked") public static <T> Enumeration<T> emptyEnumeration() { return (Enumeration<T>) EmptyEnumeration.EMPTY_ENUMERATION; } private static class EmptyEnumeration<E> implements Enumeration<E> { static final EmptyEnumeration<Object> EMPTY_ENUMERATION = new EmptyEnumeration<>(); public boolean hasMoreElements() { return false; } public E nextElement() { throw new NoSuchElementException(); } public Iterator<E> asIterator() { return emptyIterator(); } } /** * The empty set (immutable). This set is serializable. * * @see #emptySet() */ @SuppressWarnings("rawtypes") public static final Set EMPTY_SET = new EmptySet<>(); /** * Returns an empty set (immutable). This set is serializable. * Unlike the like-named field, this method is parameterized. * * <p>This example illustrates the type-safe way to obtain an empty set: * <pre> * Set<String> s = Collections.emptySet(); * </pre> * @implNote Implementations of this method need not create a separate * {@code Set} object for each call. Using this method is likely to have * comparable cost to using the like-named field. (Unlike this method, the * field does not provide type safety.) * * @param <T> the class of the objects in the set * @return the empty set * * @see #EMPTY_SET * @since 1.5 */ @SuppressWarnings("unchecked") public static final <T> Set<T> emptySet() { return (Set<T>) EMPTY_SET; } /** * @serial include */ private static class EmptySet<E> extends AbstractSet<E> implements Serializable { private static final long serialVersionUID = 1582296315990362920L; public Iterator<E> iterator() { return emptyIterator(); } public int size() { return 0; } public boolean isEmpty() { return true; } public void clear() { } public boolean contains(Object obj) { return false; } public boolean containsAll(Collection<?> c) { return c.isEmpty(); } public Object[] toArray() { return new Object[0]; } public <T> T[] toArray(T[] a) { if (a.length > 0) a[0] = null; return a; } // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); } @Override public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); return false; } @Override public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } // Preserves singleton property private Object readResolve() { return EMPTY_SET; } @Override public int hashCode() { return 0; } } /** * Returns an empty sorted set (immutable). This set is serializable. * * <p>This example illustrates the type-safe way to obtain an empty * sorted set: * <pre> {@code * SortedSet<String> s = Collections.emptySortedSet(); * }</pre> * * @implNote Implementations of this method need not create a separate * {@code SortedSet} object for each call. * * @param <E> type of elements, if there were any, in the set * @return the empty sorted set * @since 1.8 */ @SuppressWarnings("unchecked") public static <E> SortedSet<E> emptySortedSet() { return (SortedSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; } /** * Returns an empty navigable set (immutable). This set is serializable. * * <p>This example illustrates the type-safe way to obtain an empty * navigable set: * <pre> {@code * NavigableSet<String> s = Collections.emptyNavigableSet(); * }</pre> * * @implNote Implementations of this method need not * create a separate {@code NavigableSet} object for each call. * * @param <E> type of elements, if there were any, in the set * @return the empty navigable set * @since 1.8 */ @SuppressWarnings("unchecked") public static <E> NavigableSet<E> emptyNavigableSet() { return (NavigableSet<E>) UnmodifiableNavigableSet.EMPTY_NAVIGABLE_SET; } /** * The empty list (immutable). This list is serializable. * * @see #emptyList() */ @SuppressWarnings("rawtypes") public static final List EMPTY_LIST = new EmptyList<>(); /** * Returns an empty list (immutable). This list is serializable. * * <p>This example illustrates the type-safe way to obtain an empty list: * <pre> * List<String> s = Collections.emptyList(); * </pre> * * @implNote * Implementations of this method need not create a separate {@code List} * object for each call. Using this method is likely to have comparable * cost to using the like-named field. (Unlike this method, the field does * not provide type safety.) * * @param <T> type of elements, if there were any, in the list * @return an empty immutable list * * @see #EMPTY_LIST * @since 1.5 */ @SuppressWarnings("unchecked") public static final <T> List<T> emptyList() { return (List<T>) EMPTY_LIST; } /** * @serial include */ private static class EmptyList<E> extends AbstractList<E> implements RandomAccess, Serializable { private static final long serialVersionUID = 8842843931221139166L; public Iterator<E> iterator() { return emptyIterator(); } public ListIterator<E> listIterator() { return emptyListIterator(); } public int size() { return 0; } public boolean isEmpty() { return true; } public void clear() { } public boolean contains(Object obj) { return false; } public boolean containsAll(Collection<?> c) { return c.isEmpty(); } public Object[] toArray() { return new Object[0]; } public <T> T[] toArray(T[] a) { if (a.length > 0) a[0] = null; return a; } public E get(int index) { throw new IndexOutOfBoundsException("Index: " + index); } public boolean equals(Object o) { return (o instanceof List) && ((List<?>) o).isEmpty(); } public int hashCode() { return 1; } @Override public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); return false; } @Override public void replaceAll(UnaryOperator<E> operator) { Objects.requireNonNull(operator); } @Override public void sort(Comparator<? super E> c) { } // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); } @Override public Spliterator<E> spliterator() { return Spliterators.emptySpliterator(); } // Preserves singleton property private Object readResolve() { return EMPTY_LIST; } } /** * The empty map (immutable). This map is serializable. * * @see #emptyMap() * @since 1.3 */ @SuppressWarnings("rawtypes") public static final Map EMPTY_MAP = new EmptyMap<>(); /** * Returns an empty map (immutable). This map is serializable. * * <p>This example illustrates the type-safe way to obtain an empty map: * <pre> * Map<String, Date> s = Collections.emptyMap(); * </pre> * @implNote Implementations of this method need not create a separate * {@code Map} object for each call. Using this method is likely to have * comparable cost to using the like-named field. (Unlike this method, the * field does not provide type safety.) * * @param <K> the class of the map keys * @param <V> the class of the map values * @return an empty map * @see #EMPTY_MAP * @since 1.5 */ @SuppressWarnings("unchecked") public static final <K, V> Map<K, V> emptyMap() { return (Map<K, V>) EMPTY_MAP; } /** * Returns an empty sorted map (immutable). This map is serializable. * * <p>This example illustrates the type-safe way to obtain an empty map: * <pre> {@code * SortedMap<String, Date> s = Collections.emptySortedMap(); * }</pre> * * @implNote Implementations of this method need not create a separate * {@code SortedMap} object for each call. * * @param <K> the class of the map keys * @param <V> the class of the map values * @return an empty sorted map * @since 1.8 */ @SuppressWarnings("unchecked") public static final <K, V> SortedMap<K, V> emptySortedMap() { return (SortedMap<K, V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; } /** * Returns an empty navigable map (immutable). This map is serializable. * * <p>This example illustrates the type-safe way to obtain an empty map: * <pre> {@code * NavigableMap<String, Date> s = Collections.emptyNavigableMap(); * }</pre> * * @implNote Implementations of this method need not create a separate * {@code NavigableMap} object for each call. * * @param <K> the class of the map keys * @param <V> the class of the map values * @return an empty navigable map * @since 1.8 */ @SuppressWarnings("unchecked") public static final <K, V> NavigableMap<K, V> emptyNavigableMap() { return (NavigableMap<K, V>) UnmodifiableNavigableMap.EMPTY_NAVIGABLE_MAP; } /** * @serial include */ private static class EmptyMap<K, V> extends AbstractMap<K, V> implements Serializable { private static final long serialVersionUID = 6428348081105594320L; public int size() { return 0; } public boolean isEmpty() { return true; } public void clear() { } public boolean containsKey(Object key) { return false; } public boolean containsValue(Object value) { return false; } public V get(Object key) { return null; } public Set<K> keySet() { return emptySet(); } public Collection<V> values() { return emptySet(); } public Set<Map.Entry<K, V>> entrySet() { return emptySet(); } public boolean equals(Object o) { return (o instanceof Map) && ((Map<?, ?>) o).isEmpty(); } public int hashCode() { return 0; } // Override default methods in Map @Override @SuppressWarnings("unchecked") public V getOrDefault(Object k, V defaultValue) { return defaultValue; } @Override public void forEach(BiConsumer<? super K, ? super V> action) { Objects.requireNonNull(action); } @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { Objects.requireNonNull(function); } @Override public V putIfAbsent(K key, V value) { throw new UnsupportedOperationException(); } @Override public boolean remove(Object key, Object value) { throw new UnsupportedOperationException(); } @Override public boolean replace(K key, V oldValue, V newValue) { throw new UnsupportedOperationException(); } @Override public V replace(K key, V value) { throw new UnsupportedOperationException(); } @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { throw new UnsupportedOperationException(); } @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } // Preserves singleton property private Object readResolve() { return EMPTY_MAP; } } // Singleton collections /** * Returns an immutable set containing only the specified object. * The returned set is serializable. * * @param <T> the class of the objects in the set * @param o the sole object to be stored in the returned set. * @return an immutable set containing only the specified object. */ public static <T> Set<T> singleton(T o) { return new SingletonSet<>(o); } static <E> Iterator<E> singletonIterator(final E e) { return new Iterator<E>() { private boolean hasNext = true; public boolean hasNext() { return hasNext; } public E next() { if (hasNext) { hasNext = false; return e; } throw new NoSuchElementException(); } public void remove() { throw new UnsupportedOperationException(); } @Override public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); if (hasNext) { hasNext = false; action.accept(e); } } }; } /** * Creates a {@code Spliterator} with only the specified element * * @param <T> Type of elements * @return A singleton {@code Spliterator} */ static <T> Spliterator<T> singletonSpliterator(final T element) { return new Spliterator<T>() { long est = 1; @Override public Spliterator<T> trySplit() { return null; } @Override public boolean tryAdvance(Consumer<? super T> consumer) { Objects.requireNonNull(consumer); if (est > 0) { est--; consumer.accept(element); return true; } return false; } @Override public void forEachRemaining(Consumer<? super T> consumer) { tryAdvance(consumer); } @Override public long estimateSize() { return est; } @Override public int characteristics() { int value = (element != null) ? Spliterator.NONNULL : 0; return value | Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.IMMUTABLE | Spliterator.DISTINCT | Spliterator.ORDERED; } }; } /** * @serial include */ private static class SingletonSet<E> extends AbstractSet<E> implements Serializable { private static final long serialVersionUID = 3193687207550431679L; private final E element; SingletonSet(E e) { element = e; } public Iterator<E> iterator() { return singletonIterator(element); } public int size() { return 1; } public boolean contains(Object o) { return eq(o, element); } // Override default methods for Collection @Override public void forEach(Consumer<? super E> action) { action.accept(element); } @Override public Spliterator<E> spliterator() { return singletonSpliterator(element); } @Override public boolean removeIf(Predicate<? super E> filter) { throw new UnsupportedOperationException(); } @Override public int hashCode() { return Objects.hashCode(element); } } /** * Returns an immutable list containing only the specified object. * The returned list is serializable. * * @param <T> the class of the objects in the list * @param o the sole object to be stored in the returned list. * @return an immutable list containing only the specified object. * @since 1.3 */ public static <T> List<T> singletonList(T o) { return new SingletonList<>(o); } /** * @serial include */ private static class SingletonList<E> extends AbstractList<E> implements RandomAccess, Serializable { private static final long serialVersionUID = 3093736618740652951L; private final E element; SingletonList(E obj) { element = obj; } public Iterator<E> iterator() { return singletonIterator(element); } public int size() { return 1; } public boolean contains(Object obj) { return eq(obj, element); } public E get(int index) { if (index != 0) throw new IndexOutOfBoundsException("Index: " + index + ", Size: 1"); return element; } // Override default methods for Collection @Override public void forEach(Consumer<? super E> action) { action.accept(element); } @Override public boolean removeIf(Predicate<? super E> filter) { throw new UnsupportedOperationException(); } @Override public void replaceAll(UnaryOperator<E> operator) { throw new UnsupportedOperationException(); } @Override public void sort(Comparator<? super E> c) { } @Override public Spliterator<E> spliterator() { return singletonSpliterator(element); } @Override public int hashCode() { return 31 + Objects.hashCode(element); } } /** * Returns an immutable map, mapping only the specified key to the * specified value. The returned map is serializable. * * @param <K> the class of the map keys * @param <V> the class of the map values * @param key the sole key to be stored in the returned map. * @param value the value to which the returned map maps {@code key}. * @return an immutable map containing only the specified key-value * mapping. * @since 1.3 */ public static <K, V> Map<K, V> singletonMap(K key, V value) { return new SingletonMap<>(key, value); } /** * @serial include */ private static class SingletonMap<K, V> extends AbstractMap<K, V> implements Serializable { private static final long serialVersionUID = -6979724477215052911L; private final K k; private final V v; SingletonMap(K key, V value) { k = key; v = value; } public int size() { return 1; } public boolean isEmpty() { return false; } public boolean containsKey(Object key) { return eq(key, k); } public boolean containsValue(Object value) { return eq(value, v); } public V get(Object key) { return (eq(key, k) ? v : null); } private transient Set<K> keySet; private transient Set<Map.Entry<K, V>> entrySet; private transient Collection<V> values; public Set<K> keySet() { if (keySet == null) keySet = singleton(k); return keySet; } public Set<Map.Entry<K, V>> entrySet() { if (entrySet == null) entrySet = Collections.<Map.Entry<K, V>>singleton(new SimpleImmutableEntry<>(k, v)); return entrySet; } public Collection<V> values() { if (values == null) values = singleton(v); return values; } // Override default methods in Map @Override public V getOrDefault(Object key, V defaultValue) { return eq(key, k) ? v : defaultValue; } @Override public void forEach(BiConsumer<? super K, ? super V> action) { action.accept(k, v); } @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { throw new UnsupportedOperationException(); } @Override public V putIfAbsent(K key, V value) { throw new UnsupportedOperationException(); } @Override public boolean remove(Object key, Object value) { throw new UnsupportedOperationException(); } @Override public boolean replace(K key, V oldValue, V newValue) { throw new UnsupportedOperationException(); } @Override public V replace(K key, V value) { throw new UnsupportedOperationException(); } @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { throw new UnsupportedOperationException(); } @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { throw new UnsupportedOperationException(); } @Override public int hashCode() { return Objects.hashCode(k) ^ Objects.hashCode(v); } } // Miscellaneous /** * Returns an immutable list consisting of {@code n} copies of the * specified object. The newly allocated data object is tiny (it contains * a single reference to the data object). This method is useful in * combination with the {@code List.addAll} method to grow lists. * The returned list is serializable. * * @param <T> the class of the object to copy and of the objects * in the returned list. * @param n the number of elements in the returned list. * @param o the element to appear repeatedly in the returned list. * @return an immutable list consisting of {@code n} copies of the * specified object. * @throws IllegalArgumentException if {@code n < 0} * @see List#addAll(Collection) * @see List#addAll(int, Collection) */ public static <T> List<T> nCopies(int n, T o) { if (n < 0) throw new IllegalArgumentException("List length = " + n); return new CopiesList<>(n, o); } /** * @serial include */ private static class CopiesList<E> extends AbstractList<E> implements RandomAccess, Serializable { private static final long serialVersionUID = 2739099268398711800L; final int n; final E element; CopiesList(int n, E e) { assert n >= 0; this.n = n; element = e; } public int size() { return n; } public boolean contains(Object obj) { return n != 0 && eq(obj, element); } public int indexOf(Object o) { return contains(o) ? 0 : -1; } public int lastIndexOf(Object o) { return contains(o) ? n - 1 : -1; } public E get(int index) { if (index < 0 || index >= n) throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + n); return element; } public Object[] toArray() { final Object[] a = new Object[n]; if (element != null) Arrays.fill(a, 0, n, element); return a; } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { final int n = this.n; if (a.length < n) { a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), n); if (element != null) Arrays.fill(a, 0, n, element); } else { Arrays.fill(a, 0, n, element); if (a.length > n) a[n] = null; } return a; } public List<E> subList(int fromIndex, int toIndex) { if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); if (toIndex > n) throw new IndexOutOfBoundsException("toIndex = " + toIndex); if (fromIndex > toIndex) throw new IllegalArgumentException("fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")"); return new CopiesList<>(toIndex - fromIndex, element); } @Override public int hashCode() { if (n == 0) return 1; // hashCode of n repeating elements is 31^n + elementHash * Sum(31^k, k = 0..n-1) // this implementation completes in O(log(n)) steps taking advantage of // 31^(2*n) = (31^n)^2 and Sum(31^k, k = 0..(2*n-1)) = Sum(31^k, k = 0..n-1) * (31^n + 1) int pow = 31; int sum = 1; for (int i = Integer.numberOfLeadingZeros(n) + 1; i < Integer.SIZE; i++) { sum *= pow + 1; pow *= pow; if ((n << i) < 0) { pow *= 31; sum = sum * 31 + 1; } } return pow + sum * (element == null ? 0 : element.hashCode()); } @Override public boolean equals(Object o) { if (o == this) return true; if (o instanceof CopiesList) { CopiesList<?> other = (CopiesList<?>) o; return n == other.n && (n == 0 || eq(element, other.element)); } if (!(o instanceof List)) return false; int remaining = n; E e = element; Iterator<?> itr = ((List<?>) o).iterator(); if (e == null) { while (itr.hasNext() && remaining-- > 0) { if (itr.next() != null) return false; } } else { while (itr.hasNext() && remaining-- > 0) { if (!e.equals(itr.next())) return false; } } return remaining == 0 && !itr.hasNext(); } // Override default methods in Collection @Override public Stream<E> stream() { return IntStream.range(0, n).mapToObj(i -> element); } @Override public Stream<E> parallelStream() { return IntStream.range(0, n).parallel().mapToObj(i -> element); } @Override public Spliterator<E> spliterator() { return stream().spliterator(); } } /** * Returns a comparator that imposes the reverse of the <em>natural * ordering</em> on a collection of objects that implement the * {@code Comparable} interface. (The natural ordering is the ordering * imposed by the objects' own {@code compareTo} method.) This enables a * simple idiom for sorting (or maintaining) collections (or arrays) of * objects that implement the {@code Comparable} interface in * reverse-natural-order. For example, suppose {@code a} is an array of * strings. Then: <pre> * Arrays.sort(a, Collections.reverseOrder()); * </pre> sorts the array in reverse-lexicographic (alphabetical) order.<p> * * The returned comparator is serializable. * * @param <T> the class of the objects compared by the comparator * @return A comparator that imposes the reverse of the <i>natural * ordering</i> on a collection of objects that implement * the {@code Comparable} interface. * @see Comparable */ @SuppressWarnings("unchecked") public static <T> Comparator<T> reverseOrder() { return (Comparator<T>) ReverseComparator.REVERSE_ORDER; } /** * @serial include */ private static class ReverseComparator implements Comparator<Comparable<Object>>, Serializable { private static final long serialVersionUID = 7207038068494060240L; static final ReverseComparator REVERSE_ORDER = new ReverseComparator(); public int compare(Comparable<Object> c1, Comparable<Object> c2) { return c2.compareTo(c1); } private Object readResolve() { return Collections.reverseOrder(); } @Override public Comparator<Comparable<Object>> reversed() { return Comparator.naturalOrder(); } } /** * Returns a comparator that imposes the reverse ordering of the specified * comparator. If the specified comparator is {@code null}, this method is * equivalent to {@link #reverseOrder()} (in other words, it returns a * comparator that imposes the reverse of the <em>natural ordering</em> on * a collection of objects that implement the Comparable interface). * * <p>The returned comparator is serializable (assuming the specified * comparator is also serializable or {@code null}). * * @param <T> the class of the objects compared by the comparator * @param cmp a comparator who's ordering is to be reversed by the returned * comparator or {@code null} * @return A comparator that imposes the reverse ordering of the * specified comparator. * @since 1.5 */ @SuppressWarnings("unchecked") public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) { if (cmp == null) { return (Comparator<T>) ReverseComparator.REVERSE_ORDER; } else if (cmp == ReverseComparator.REVERSE_ORDER) { return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE; } else if (cmp == Comparators.NaturalOrderComparator.INSTANCE) { return (Comparator<T>) ReverseComparator.REVERSE_ORDER; } else if (cmp instanceof ReverseComparator2) { return ((ReverseComparator2<T>) cmp).cmp; } else { return new ReverseComparator2<>(cmp); } } /** * @serial include */ private static class ReverseComparator2<T> implements Comparator<T>, Serializable { private static final long serialVersionUID = 4374092139857L; /** * The comparator specified in the static factory. This will never * be null, as the static factory returns a ReverseComparator * instance if its argument is null. * * @serial */ final Comparator<T> cmp; ReverseComparator2(Comparator<T> cmp) { assert cmp != null; this.cmp = cmp; } public int compare(T t1, T t2) { return cmp.compare(t2, t1); } public boolean equals(Object o) { return (o == this) || (o instanceof ReverseComparator2 && cmp.equals(((ReverseComparator2) o).cmp)); } public int hashCode() { return cmp.hashCode() ^ Integer.MIN_VALUE; } @Override public Comparator<T> reversed() { return cmp; } } /** * Returns an enumeration over the specified collection. This provides * interoperability with legacy APIs that require an enumeration * as input. * * <p>The iterator returned from a call to {@link Enumeration#asIterator()} * does not support removal of elements from the specified collection. This * is necessary to avoid unintentionally increasing the capabilities of the * returned enumeration. * * @param <T> the class of the objects in the collection * @param c the collection for which an enumeration is to be returned. * @return an enumeration over the specified collection. * @see Enumeration */ public static <T> Enumeration<T> enumeration(final Collection<T> c) { return new Enumeration<T>() { private final Iterator<T> i = c.iterator(); public boolean hasMoreElements() { return i.hasNext(); } public T nextElement() { return i.next(); } }; } /** * Returns an array list containing the elements returned by the * specified enumeration in the order they are returned by the * enumeration. This method provides interoperability between * legacy APIs that return enumerations and new APIs that require * collections. * * @param <T> the class of the objects returned by the enumeration * @param e enumeration providing elements for the returned * array list * @return an array list containing the elements returned * by the specified enumeration. * @since 1.4 * @see Enumeration * @see ArrayList */ public static <T> ArrayList<T> list(Enumeration<T> e) { ArrayList<T> l = new ArrayList<>(); while (e.hasMoreElements()) l.add(e.nextElement()); return l; } /** * Returns true if the specified arguments are equal, or both null. * * NB: Do not replace with Object.equals until JDK-8015417 is resolved. */ static boolean eq(Object o1, Object o2) { return o1 == null ? o2 == null : o1.equals(o2); } /** * Returns the number of elements in the specified collection equal to the * specified object. More formally, returns the number of elements * {@code e} in the collection such that * {@code Objects.equals(o, e)}. * * @param c the collection in which to determine the frequency * of {@code o} * @param o the object whose frequency is to be determined * @return the number of elements in {@code c} equal to {@code o} * @throws NullPointerException if {@code c} is null * @since 1.5 */ public static int frequency(Collection<?> c, Object o) { int result = 0; if (o == null) { for (Object e : c) if (e == null) result++; } else { for (Object e : c) if (o.equals(e)) result++; } return result; } /** * Returns {@code true} if the two specified collections have no * elements in common. * * <p>Care must be exercised if this method is used on collections that * do not comply with the general contract for {@code Collection}. * Implementations may elect to iterate over either collection and test * for containment in the other collection (or to perform any equivalent * computation). If either collection uses a nonstandard equality test * (as does a {@link SortedSet} whose ordering is not <em>compatible with * equals</em>, or the key set of an {@link IdentityHashMap}), both * collections must use the same nonstandard equality test, or the * result of this method is undefined. * * <p>Care must also be exercised when using collections that have * restrictions on the elements that they may contain. Collection * implementations are allowed to throw exceptions for any operation * involving elements they deem ineligible. For absolute safety the * specified collections should contain only elements which are * eligible elements for both collections. * * <p>Note that it is permissible to pass the same collection in both * parameters, in which case the method will return {@code true} if and * only if the collection is empty. * * @param c1 a collection * @param c2 a collection * @return {@code true} if the two specified collections have no * elements in common. * @throws NullPointerException if either collection is {@code null}. * @throws NullPointerException if one collection contains a {@code null} * element and {@code null} is not an eligible element for the other collection. * (<a href="Collection.html#optional-restrictions">optional</a>) * @throws ClassCastException if one collection contains an element that is * of a type which is ineligible for the other collection. * (<a href="Collection.html#optional-restrictions">optional</a>) * @since 1.5 */ public static boolean disjoint(Collection<?> c1, Collection<?> c2) { // The collection to be used for contains(). Preference is given to // the collection who's contains() has lower O() complexity. Collection<?> contains = c2; // The collection to be iterated. If the collections' contains() impl // are of different O() complexity, the collection with slower // contains() will be used for iteration. For collections who's // contains() are of the same complexity then best performance is // achieved by iterating the smaller collection. Collection<?> iterate = c1; // Performance optimization cases. The heuristics: // 1. Generally iterate over c1. // 2. If c1 is a Set then iterate over c2. // 3. If either collection is empty then result is always true. // 4. Iterate over the smaller Collection. if (c1 instanceof Set) { // Use c1 for contains as a Set's contains() is expected to perform // better than O(N/2) iterate = c2; contains = c1; } else if (!(c2 instanceof Set)) { // Both are mere Collections. Iterate over smaller collection. // Example: If c1 contains 3 elements and c2 contains 50 elements and // assuming contains() requires ceiling(N/2) comparisons then // checking for all c1 elements in c2 would require 75 comparisons // (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring // 100 comparisons (50 * ceiling(3/2)). int c1size = c1.size(); int c2size = c2.size(); if (c1size == 0 || c2size == 0) { // At least one collection is empty. Nothing will match. return true; } if (c1size > c2size) { iterate = c2; contains = c1; } } for (Object e : iterate) { if (contains.contains(e)) { // Found a common element. Collections are not disjoint. return false; } } // No common elements were found. return true; } /** * Adds all of the specified elements to the specified collection. * Elements to be added may be specified individually or as an array. * The behavior of this convenience method is identical to that of * {@code c.addAll(Arrays.asList(elements))}, but this method is likely * to run significantly faster under most implementations. * * <p>When elements are specified individually, this method provides a * convenient way to add a few elements to an existing collection: * <pre> * Collections.addAll(flavors, "Peaches 'n Plutonium", "Rocky Racoon"); * </pre> * * @param <T> the class of the elements to add and of the collection * @param c the collection into which {@code elements} are to be inserted * @param elements the elements to insert into {@code c} * @return {@code true} if the collection changed as a result of the call * @throws UnsupportedOperationException if {@code c} does not support * the {@code add} operation * @throws NullPointerException if {@code elements} contains one or more * null values and {@code c} does not permit null elements, or * if {@code c} or {@code elements} are {@code null} * @throws IllegalArgumentException if some property of a value in * {@code elements} prevents it from being added to {@code c} * @see Collection#addAll(Collection) * @since 1.5 */ @SafeVarargs public static <T> boolean addAll(Collection<? super T> c, T... elements) { boolean result = false; for (T element : elements) result |= c.add(element); return result; } /** * Returns a set backed by the specified map. The resulting set displays * the same ordering, concurrency, and performance characteristics as the * backing map. In essence, this factory method provides a {@link Set} * implementation corresponding to any {@link Map} implementation. There * is no need to use this method on a {@link Map} implementation that * already has a corresponding {@link Set} implementation (such as {@link * HashMap} or {@link TreeMap}). * * <p>Each method invocation on the set returned by this method results in * exactly one method invocation on the backing map or its {@code keySet} * view, with one exception. The {@code addAll} method is implemented * as a sequence of {@code put} invocations on the backing map. * * <p>The specified map must be empty at the time this method is invoked, * and should not be accessed directly after this method returns. These * conditions are ensured if the map is created empty, passed directly * to this method, and no reference to the map is retained, as illustrated * in the following code fragment: * <pre> * Set<Object> weakHashSet = Collections.newSetFromMap( * new WeakHashMap<Object, Boolean>()); * </pre> * * @param <E> the class of the map keys and of the objects in the * returned set * @param map the backing map * @return the set backed by the map * @throws IllegalArgumentException if {@code map} is not empty * @since 1.6 */ public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) { return new SetFromMap<>(map); } /** * @serial include */ private static class SetFromMap<E> extends AbstractSet<E> implements Set<E>, Serializable { private final Map<E, Boolean> m; // The backing map private transient Set<E> s; // Its keySet SetFromMap(Map<E, Boolean> map) { if (!map.isEmpty()) throw new IllegalArgumentException("Map is non-empty"); m = map; s = map.keySet(); } public void clear() { m.clear(); } public int size() { return m.size(); } public boolean isEmpty() { return m.isEmpty(); } public boolean contains(Object o) { return m.containsKey(o); } public boolean remove(Object o) { return m.remove(o) != null; } public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; } public Iterator<E> iterator() { return s.iterator(); } public Object[] toArray() { return s.toArray(); } public <T> T[] toArray(T[] a) { return s.toArray(a); } public String toString() { return s.toString(); } public int hashCode() { return s.hashCode(); } public boolean equals(Object o) { return o == this || s.equals(o); } public boolean containsAll(Collection<?> c) { return s.containsAll(c); } public boolean removeAll(Collection<?> c) { return s.removeAll(c); } public boolean retainAll(Collection<?> c) { return s.retainAll(c); } // addAll is the only inherited implementation // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { s.forEach(action); } @Override public boolean removeIf(Predicate<? super E> filter) { return s.removeIf(filter); } @Override public Spliterator<E> spliterator() { return s.spliterator(); } @Override public Stream<E> stream() { return s.stream(); } @Override public Stream<E> parallelStream() { return s.parallelStream(); } private static final long serialVersionUID = 2454657854757543876L; private void readObject(java.io.ObjectInputStream stream) throws IOException, ClassNotFoundException { stream.defaultReadObject(); s = m.keySet(); } } /** * Returns a view of a {@link Deque} as a Last-in-first-out (Lifo) * {@link Queue}. Method {@code add} is mapped to {@code push}, * {@code remove} is mapped to {@code pop} and so on. This * view can be useful when you would like to use a method * requiring a {@code Queue} but you need Lifo ordering. * * <p>Each method invocation on the queue returned by this method * results in exactly one method invocation on the backing deque, with * one exception. The {@link Queue#addAll addAll} method is * implemented as a sequence of {@link Deque#addFirst addFirst} * invocations on the backing deque. * * @param <T> the class of the objects in the deque * @param deque the deque * @return the queue * @since 1.6 */ public static <T> Queue<T> asLifoQueue(Deque<T> deque) { return new AsLIFOQueue<>(Objects.requireNonNull(deque)); } /** * @serial include */ static class AsLIFOQueue<E> extends AbstractQueue<E> implements Queue<E>, Serializable { private static final long serialVersionUID = 1802017725587941708L; private final Deque<E> q; AsLIFOQueue(Deque<E> q) { this.q = q; } public boolean add(E e) { q.addFirst(e); return true; } public boolean offer(E e) { return q.offerFirst(e); } public E poll() { return q.pollFirst(); } public E remove() { return q.removeFirst(); } public E peek() { return q.peekFirst(); } public E element() { return q.getFirst(); } public void clear() { q.clear(); } public int size() { return q.size(); } public boolean isEmpty() { return q.isEmpty(); } public boolean contains(Object o) { return q.contains(o); } public boolean remove(Object o) { return q.remove(o); } public Iterator<E> iterator() { return q.iterator(); } public Object[] toArray() { return q.toArray(); } public <T> T[] toArray(T[] a) { return q.toArray(a); } public <T> T[] toArray(IntFunction<T[]> f) { return q.toArray(f); } public String toString() { return q.toString(); } public boolean containsAll(Collection<?> c) { return q.containsAll(c); } public boolean removeAll(Collection<?> c) { return q.removeAll(c); } public boolean retainAll(Collection<?> c) { return q.retainAll(c); } // We use inherited addAll; forwarding addAll would be wrong // Override default methods in Collection @Override public void forEach(Consumer<? super E> action) { q.forEach(action); } @Override public boolean removeIf(Predicate<? super E> filter) { return q.removeIf(filter); } @Override public Spliterator<E> spliterator() { return q.spliterator(); } @Override public Stream<E> stream() { return q.stream(); } @Override public Stream<E> parallelStream() { return q.parallelStream(); } } }