Java tutorial
/* * 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. */ /* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group. Adapted and released, under explicit permission, * from JDK ArrayList.java which carries the following copyright: * * Copyright 1997 by Sun Microsystems, Inc., * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A. * All rights reserved. */ package java.util.concurrent; import java.lang.invoke.VarHandle; import java.lang.reflect.Field; import java.util.Arrays; import java.util.Collection; import java.util.Comparator; import java.util.ConcurrentModificationException; import java.util.Iterator; import java.util.List; import java.util.ListIterator; import java.util.NoSuchElementException; import java.util.Objects; import java.util.RandomAccess; import java.util.Spliterator; import java.util.Spliterators; import java.util.function.Consumer; import java.util.function.Predicate; import java.util.function.UnaryOperator; import jdk.internal.access.SharedSecrets; /** * A thread-safe variant of {@link java.util.ArrayList} in which all mutative * operations ({@code add}, {@code set}, and so on) are implemented by * making a fresh copy of the underlying array. * * <p>This is ordinarily too costly, but may be <em>more</em> efficient * than alternatives when traversal operations vastly outnumber * mutations, and is useful when you cannot or don't want to * synchronize traversals, yet need to preclude interference among * concurrent threads. The "snapshot" style iterator method uses a * reference to the state of the array at the point that the iterator * was created. This array never changes during the lifetime of the * iterator, so interference is impossible and the iterator is * guaranteed not to throw {@code ConcurrentModificationException}. * The iterator will not reflect additions, removals, or changes to * the list since the iterator was created. Element-changing * operations on iterators themselves ({@code remove}, {@code set}, and * {@code add}) are not supported. These methods throw * {@code UnsupportedOperationException}. * * <p>All elements are permitted, including {@code null}. * * <p>Memory consistency effects: As with other concurrent * collections, actions in a thread prior to placing an object into a * {@code CopyOnWriteArrayList} * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> * actions subsequent to the access or removal of that element from * the {@code CopyOnWriteArrayList} in another thread. * * <p>This class is a member of the * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> * Java Collections Framework</a>. * * @since 1.5 * @author Doug Lea * @param <E> the type of elements held in this list */ public class CopyOnWriteArrayList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable { private static final long serialVersionUID = 8673264195747942595L; /** * The lock protecting all mutators. (We have a mild preference * for builtin monitors over ReentrantLock when either will do.) */ final transient Object lock = new Object(); /** The array, accessed only via getArray/setArray. */ private transient volatile Object[] array; /** * Gets the array. Non-private so as to also be accessible * from CopyOnWriteArraySet class. */ final Object[] getArray() { return array; } /** * Sets the array. */ final void setArray(Object[] a) { array = a; } /** * Creates an empty list. */ public CopyOnWriteArrayList() { setArray(new Object[0]); } /** * Creates a list containing the elements of the specified * collection, in the order they are returned by the collection's * iterator. * * @param c the collection of initially held elements * @throws NullPointerException if the specified collection is null */ public CopyOnWriteArrayList(Collection<? extends E> c) { Object[] es; if (c.getClass() == CopyOnWriteArrayList.class) es = ((CopyOnWriteArrayList<?>) c).getArray(); else { es = c.toArray(); // defend against c.toArray (incorrectly) not returning Object[] // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652) if (es.getClass() != Object[].class) es = Arrays.copyOf(es, es.length, Object[].class); } setArray(es); } /** * Creates a list holding a copy of the given array. * * @param toCopyIn the array (a copy of this array is used as the * internal array) * @throws NullPointerException if the specified array is null */ public CopyOnWriteArrayList(E[] toCopyIn) { setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class)); } /** * Returns the number of elements in this list. * * @return the number of elements in this list */ public int size() { return getArray().length; } /** * Returns {@code true} if this list contains no elements. * * @return {@code true} if this list contains no elements */ public boolean isEmpty() { return size() == 0; } /** * static version of indexOf, to allow repeated calls without * needing to re-acquire array each time. * @param o element to search for * @param es the array * @param from first index to search * @param to one past last index to search * @return index of element, or -1 if absent */ private static int indexOfRange(Object o, Object[] es, int from, int to) { if (o == null) { for (int i = from; i < to; i++) if (es[i] == null) return i; } else { for (int i = from; i < to; i++) if (o.equals(es[i])) return i; } return -1; } /** * static version of lastIndexOf. * @param o element to search for * @param es the array * @param from index of first element of range, last element to search * @param to one past last element of range, first element to search * @return index of element, or -1 if absent */ private static int lastIndexOfRange(Object o, Object[] es, int from, int to) { if (o == null) { for (int i = to - 1; i >= from; i--) if (es[i] == null) return i; } else { for (int i = to - 1; i >= from; i--) if (o.equals(es[i])) return i; } return -1; } /** * Returns {@code true} if this list contains the specified element. * More formally, returns {@code true} if and only if this list contains * at least one element {@code e} such that {@code Objects.equals(o, e)}. * * @param o element whose presence in this list is to be tested * @return {@code true} if this list contains the specified element */ public boolean contains(Object o) { return indexOf(o) >= 0; } /** * {@inheritDoc} */ public int indexOf(Object o) { Object[] es = getArray(); return indexOfRange(o, es, 0, es.length); } /** * Returns the index of the first occurrence of the specified element in * this list, searching forwards from {@code index}, or returns -1 if * the element is not found. * More formally, returns the lowest index {@code i} such that * {@code i >= index && Objects.equals(get(i), e)}, * or -1 if there is no such index. * * @param e element to search for * @param index index to start searching from * @return the index of the first occurrence of the element in * this list at position {@code index} or later in the list; * {@code -1} if the element is not found. * @throws IndexOutOfBoundsException if the specified index is negative */ public int indexOf(E e, int index) { Object[] es = getArray(); return indexOfRange(e, es, index, es.length); } /** * {@inheritDoc} */ public int lastIndexOf(Object o) { Object[] es = getArray(); return lastIndexOfRange(o, es, 0, es.length); } /** * Returns the index of the last occurrence of the specified element in * this list, searching backwards from {@code index}, or returns -1 if * the element is not found. * More formally, returns the highest index {@code i} such that * {@code i <= index && Objects.equals(get(i), e)}, * or -1 if there is no such index. * * @param e element to search for * @param index index to start searching backwards from * @return the index of the last occurrence of the element at position * less than or equal to {@code index} in this list; * -1 if the element is not found. * @throws IndexOutOfBoundsException if the specified index is greater * than or equal to the current size of this list */ public int lastIndexOf(E e, int index) { Object[] es = getArray(); return lastIndexOfRange(e, es, 0, index + 1); } /** * Returns a shallow copy of this list. (The elements themselves * are not copied.) * * @return a clone of this list */ public Object clone() { try { @SuppressWarnings("unchecked") CopyOnWriteArrayList<E> clone = (CopyOnWriteArrayList<E>) super.clone(); clone.resetLock(); // Unlike in readObject, here we cannot visibility-piggyback on the // volatile write in setArray(). VarHandle.releaseFence(); return clone; } catch (CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneable throw new InternalError(); } } /** * Returns an array containing all of the elements in this list * in proper sequence (from first to last element). * * <p>The returned array will be "safe" in that no references to it are * maintained by this list. (In other words, this method must allocate * a new array). The caller is thus free to modify the returned array. * * <p>This method acts as bridge between array-based and collection-based * APIs. * * @return an array containing all the elements in this list */ public Object[] toArray() { return getArray().clone(); } /** * Returns an array containing all of the elements in this list in * proper sequence (from first to last element); the runtime type of * the returned array is that of the specified array. If the list fits * in the specified array, it is returned therein. Otherwise, a new * array is allocated with the runtime type of the specified array and * the size of this list. * * <p>If this list fits in the specified array with room to spare * (i.e., the array has more elements than this list), the element in * the array immediately following the end of the list is set to * {@code null}. (This is useful in determining the length of this * list <i>only</i> if the caller knows that this list does not contain * any null elements.) * * <p>Like the {@link #toArray()} method, this method acts as bridge between * array-based and collection-based APIs. Further, this method allows * precise control over the runtime type of the output array, and may, * under certain circumstances, be used to save allocation costs. * * <p>Suppose {@code x} is a list known to contain only strings. * The following code can be used to dump the list into a newly * allocated array of {@code String}: * * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> * * Note that {@code toArray(new Object[0])} is identical in function to * {@code toArray()}. * * @param a the array into which the elements of the list are to * be stored, if it is big enough; otherwise, a new array of the * same runtime type is allocated for this purpose. * @return an array containing all the elements in this list * @throws ArrayStoreException if the runtime type of the specified array * is not a supertype of the runtime type of every element in * this list * @throws NullPointerException if the specified array is null */ @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { Object[] es = getArray(); int len = es.length; if (a.length < len) return (T[]) Arrays.copyOf(es, len, a.getClass()); else { System.arraycopy(es, 0, a, 0, len); if (a.length > len) a[len] = null; return a; } } // Positional Access Operations @SuppressWarnings("unchecked") static <E> E elementAt(Object[] a, int index) { return (E) a[index]; } static String outOfBounds(int index, int size) { return "Index: " + index + ", Size: " + size; } /** * {@inheritDoc} * * @throws IndexOutOfBoundsException {@inheritDoc} */ public E get(int index) { return elementAt(getArray(), index); } /** * Replaces the element at the specified position in this list with the * specified element. * * @throws IndexOutOfBoundsException {@inheritDoc} */ public E set(int index, E element) { synchronized (lock) { Object[] es = getArray(); E oldValue = elementAt(es, index); if (oldValue != element) { es = es.clone(); es[index] = element; } // Ensure volatile write semantics even when oldvalue == element setArray(es); return oldValue; } } /** * Appends the specified element to the end of this list. * * @param e element to be appended to this list * @return {@code true} (as specified by {@link Collection#add}) */ public boolean add(E e) { synchronized (lock) { Object[] es = getArray(); int len = es.length; es = Arrays.copyOf(es, len + 1); es[len] = e; setArray(es); return true; } } /** * Inserts the specified element at the specified position in this * list. Shifts the element currently at that position (if any) and * any subsequent elements to the right (adds one to their indices). * * @throws IndexOutOfBoundsException {@inheritDoc} */ public void add(int index, E element) { synchronized (lock) { Object[] es = getArray(); int len = es.length; if (index > len || index < 0) throw new IndexOutOfBoundsException(outOfBounds(index, len)); Object[] newElements; int numMoved = len - index; if (numMoved == 0) newElements = Arrays.copyOf(es, len + 1); else { newElements = new Object[len + 1]; System.arraycopy(es, 0, newElements, 0, index); System.arraycopy(es, index, newElements, index + 1, numMoved); } newElements[index] = element; setArray(newElements); } } /** * Removes the element at the specified position in this list. * Shifts any subsequent elements to the left (subtracts one from their * indices). Returns the element that was removed from the list. * * @throws IndexOutOfBoundsException {@inheritDoc} */ public E remove(int index) { synchronized (lock) { Object[] es = getArray(); int len = es.length; E oldValue = elementAt(es, index); int numMoved = len - index - 1; Object[] newElements; if (numMoved == 0) newElements = Arrays.copyOf(es, len - 1); else { newElements = new Object[len - 1]; System.arraycopy(es, 0, newElements, 0, index); System.arraycopy(es, index + 1, newElements, index, numMoved); } setArray(newElements); return oldValue; } } /** * Removes the first occurrence of the specified element from this list, * if it is present. If this list does not contain the element, it is * unchanged. More formally, removes the element with the lowest index * {@code i} such that {@code Objects.equals(o, get(i))} * (if such an element exists). Returns {@code true} if this list * contained the specified element (or equivalently, if this list * changed as a result of the call). * * @param o element to be removed from this list, if present * @return {@code true} if this list contained the specified element */ public boolean remove(Object o) { Object[] snapshot = getArray(); int index = indexOfRange(o, snapshot, 0, snapshot.length); return index >= 0 && remove(o, snapshot, index); } /** * A version of remove(Object) using the strong hint that given * recent snapshot contains o at the given index. */ private boolean remove(Object o, Object[] snapshot, int index) { synchronized (lock) { Object[] current = getArray(); int len = current.length; if (snapshot != current) findIndex: { int prefix = Math.min(index, len); for (int i = 0; i < prefix; i++) { if (current[i] != snapshot[i] && Objects.equals(o, current[i])) { index = i; break findIndex; } } if (index >= len) return false; if (current[index] == o) break findIndex; index = indexOfRange(o, current, index, len); if (index < 0) return false; } Object[] newElements = new Object[len - 1]; System.arraycopy(current, 0, newElements, 0, index); System.arraycopy(current, index + 1, newElements, index, len - index - 1); setArray(newElements); return true; } } /** * Removes from this list all of the elements whose index is between * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. * Shifts any succeeding elements to the left (reduces their index). * This call shortens the list by {@code (toIndex - fromIndex)} elements. * (If {@code toIndex==fromIndex}, this operation has no effect.) * * @param fromIndex index of first element to be removed * @param toIndex index after last element to be removed * @throws IndexOutOfBoundsException if fromIndex or toIndex out of range * ({@code fromIndex < 0 || toIndex > size() || toIndex < fromIndex}) */ void removeRange(int fromIndex, int toIndex) { synchronized (lock) { Object[] es = getArray(); int len = es.length; if (fromIndex < 0 || toIndex > len || toIndex < fromIndex) throw new IndexOutOfBoundsException(); int newlen = len - (toIndex - fromIndex); int numMoved = len - toIndex; if (numMoved == 0) setArray(Arrays.copyOf(es, newlen)); else { Object[] newElements = new Object[newlen]; System.arraycopy(es, 0, newElements, 0, fromIndex); System.arraycopy(es, toIndex, newElements, fromIndex, numMoved); setArray(newElements); } } } /** * Appends the element, if not present. * * @param e element to be added to this list, if absent * @return {@code true} if the element was added */ public boolean addIfAbsent(E e) { Object[] snapshot = getArray(); return indexOfRange(e, snapshot, 0, snapshot.length) < 0 && addIfAbsent(e, snapshot); } /** * A version of addIfAbsent using the strong hint that given * recent snapshot does not contain e. */ private boolean addIfAbsent(E e, Object[] snapshot) { synchronized (lock) { Object[] current = getArray(); int len = current.length; if (snapshot != current) { // Optimize for lost race to another addXXX operation int common = Math.min(snapshot.length, len); for (int i = 0; i < common; i++) if (current[i] != snapshot[i] && Objects.equals(e, current[i])) return false; if (indexOfRange(e, current, common, len) >= 0) return false; } Object[] newElements = Arrays.copyOf(current, len + 1); newElements[len] = e; setArray(newElements); return true; } } /** * Returns {@code true} if this list contains all of the elements of the * specified collection. * * @param c collection to be checked for containment in this list * @return {@code true} if this list contains all of the elements of the * specified collection * @throws NullPointerException if the specified collection is null * @see #contains(Object) */ public boolean containsAll(Collection<?> c) { Object[] es = getArray(); int len = es.length; for (Object e : c) { if (indexOfRange(e, es, 0, len) < 0) return false; } return true; } /** * Removes from this list all of its elements that are contained in * the specified collection. This is a particularly expensive operation * in this class because of the need for an internal temporary array. * * @param c collection containing elements to be removed from this list * @return {@code true} if this list changed as a result of the call * @throws ClassCastException if the class of an element of this list * is incompatible with the specified collection * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if this list contains a null element and the * specified collection does not permit null elements * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>), * or if the specified collection is null * @see #remove(Object) */ public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> c.contains(e)); } /** * Retains only the elements in this list that are contained in the * specified collection. In other words, removes from this list all of * its elements that are not contained in the specified collection. * * @param c collection containing elements to be retained in this list * @return {@code true} if this list changed as a result of the call * @throws ClassCastException if the class of an element of this list * is incompatible with the specified collection * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) * @throws NullPointerException if this list contains a null element and the * specified collection does not permit null elements * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>), * or if the specified collection is null * @see #remove(Object) */ public boolean retainAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> !c.contains(e)); } /** * Appends all of the elements in the specified collection that * are not already contained in this list, to the end of * this list, in the order that they are returned by the * specified collection's iterator. * * @param c collection containing elements to be added to this list * @return the number of elements added * @throws NullPointerException if the specified collection is null * @see #addIfAbsent(Object) */ public int addAllAbsent(Collection<? extends E> c) { Object[] cs = c.toArray(); if (cs.length == 0) return 0; synchronized (lock) { Object[] es = getArray(); int len = es.length; int added = 0; // uniquify and compact elements in cs for (int i = 0; i < cs.length; ++i) { Object e = cs[i]; if (indexOfRange(e, es, 0, len) < 0 && indexOfRange(e, cs, 0, added) < 0) cs[added++] = e; } if (added > 0) { Object[] newElements = Arrays.copyOf(es, len + added); System.arraycopy(cs, 0, newElements, len, added); setArray(newElements); } return added; } } /** * Removes all of the elements from this list. * The list will be empty after this call returns. */ public void clear() { synchronized (lock) { setArray(new Object[0]); } } /** * Appends all of the elements in the specified collection to the end * of this list, in the order that they are returned by the specified * collection's iterator. * * @param c collection containing elements to be added to this list * @return {@code true} if this list changed as a result of the call * @throws NullPointerException if the specified collection is null * @see #add(Object) */ public boolean addAll(Collection<? extends E> c) { Object[] cs = (c.getClass() == CopyOnWriteArrayList.class) ? ((CopyOnWriteArrayList<?>) c).getArray() : c.toArray(); if (cs.length == 0) return false; synchronized (lock) { Object[] es = getArray(); int len = es.length; Object[] newElements; if (len == 0 && cs.getClass() == Object[].class) newElements = cs; else { newElements = Arrays.copyOf(es, len + cs.length); System.arraycopy(cs, 0, newElements, len, cs.length); } setArray(newElements); return true; } } /** * Inserts all of the elements in the specified collection into this * list, starting at the specified position. Shifts the element * currently at that position (if any) and any subsequent elements to * the right (increases their indices). The new elements will appear * in this list in the order that they are returned by the * specified collection's iterator. * * @param index index at which to insert the first element * from the specified collection * @param c collection containing elements to be added to this list * @return {@code true} if this list changed as a result of the call * @throws IndexOutOfBoundsException {@inheritDoc} * @throws NullPointerException if the specified collection is null * @see #add(int,Object) */ public boolean addAll(int index, Collection<? extends E> c) { Object[] cs = c.toArray(); synchronized (lock) { Object[] es = getArray(); int len = es.length; if (index > len || index < 0) throw new IndexOutOfBoundsException(outOfBounds(index, len)); if (cs.length == 0) return false; int numMoved = len - index; Object[] newElements; if (numMoved == 0) newElements = Arrays.copyOf(es, len + cs.length); else { newElements = new Object[len + cs.length]; System.arraycopy(es, 0, newElements, 0, index); System.arraycopy(es, index, newElements, index + cs.length, numMoved); } System.arraycopy(cs, 0, newElements, index, cs.length); setArray(newElements); return true; } } /** * @throws NullPointerException {@inheritDoc} */ public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); for (Object x : getArray()) { @SuppressWarnings("unchecked") E e = (E) x; action.accept(e); } } /** * @throws NullPointerException {@inheritDoc} */ public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); return bulkRemove(filter); } // A tiny bit set implementation private static long[] nBits(int n) { return new long[((n - 1) >> 6) + 1]; } private static void setBit(long[] bits, int i) { bits[i >> 6] |= 1L << i; } private static boolean isClear(long[] bits, int i) { return (bits[i >> 6] & (1L << i)) == 0; } private boolean bulkRemove(Predicate<? super E> filter) { synchronized (lock) { return bulkRemove(filter, 0, getArray().length); } } boolean bulkRemove(Predicate<? super E> filter, int i, int end) { // assert Thread.holdsLock(lock); final Object[] es = getArray(); // Optimize for initial run of survivors for (; i < end && !filter.test(elementAt(es, i)); i++) ; if (i < end) { final int beg = i; final long[] deathRow = nBits(end - beg); int deleted = 1; deathRow[0] = 1L; // set bit 0 for (i = beg + 1; i < end; i++) if (filter.test(elementAt(es, i))) { setBit(deathRow, i - beg); deleted++; } // Did filter reentrantly modify the list? if (es != getArray()) throw new ConcurrentModificationException(); final Object[] newElts = Arrays.copyOf(es, es.length - deleted); int w = beg; for (i = beg; i < end; i++) if (isClear(deathRow, i - beg)) newElts[w++] = es[i]; System.arraycopy(es, i, newElts, w, es.length - i); setArray(newElts); return true; } else { if (es != getArray()) throw new ConcurrentModificationException(); return false; } } public void replaceAll(UnaryOperator<E> operator) { synchronized (lock) { replaceAllRange(operator, 0, getArray().length); } } void replaceAllRange(UnaryOperator<E> operator, int i, int end) { // assert Thread.holdsLock(lock); Objects.requireNonNull(operator); final Object[] es = getArray().clone(); for (; i < end; i++) es[i] = operator.apply(elementAt(es, i)); setArray(es); } public void sort(Comparator<? super E> c) { synchronized (lock) { sortRange(c, 0, getArray().length); } } @SuppressWarnings("unchecked") void sortRange(Comparator<? super E> c, int i, int end) { // assert Thread.holdsLock(lock); final Object[] es = getArray().clone(); Arrays.sort(es, i, end, (Comparator<Object>) c); setArray(es); } /** * Saves this list to a stream (that is, serializes it). * * @param s the stream * @throws java.io.IOException if an I/O error occurs * @serialData The length of the array backing the list is emitted * (int), followed by all of its elements (each an Object) * in the proper order. */ private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { s.defaultWriteObject(); Object[] es = getArray(); // Write out array length s.writeInt(es.length); // Write out all elements in the proper order. for (Object element : es) s.writeObject(element); } /** * Reconstitutes this list from a stream (that is, deserializes it). * @param s the stream * @throws ClassNotFoundException if the class of a serialized object * could not be found * @throws java.io.IOException if an I/O error occurs */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); // bind to new lock resetLock(); // Read in array length and allocate array int len = s.readInt(); SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, len); Object[] es = new Object[len]; // Read in all elements in the proper order. for (int i = 0; i < len; i++) es[i] = s.readObject(); setArray(es); } /** * Returns a string representation of this list. The string * representation consists of the string representations of the list's * elements in the order they are returned by its iterator, enclosed in * square brackets ({@code "[]"}). Adjacent elements are separated by * the characters {@code ", "} (comma and space). Elements are * converted to strings as by {@link String#valueOf(Object)}. * * @return a string representation of this list */ public String toString() { return Arrays.toString(getArray()); } /** * Compares the specified object with this list for equality. * Returns {@code true} if the specified object is the same object * as this object, or if it is also a {@link List} and the sequence * of elements returned by an {@linkplain List#iterator() iterator} * over the specified list is the same as the sequence returned by * an iterator over this list. The two sequences are considered to * be the same if they have the same length and corresponding * elements at the same position in the sequence are <em>equal</em>. * Two elements {@code e1} and {@code e2} are considered * <em>equal</em> if {@code Objects.equals(e1, e2)}. * * @param o the object to be compared for equality with this list * @return {@code true} if the specified object is equal to this list */ public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof List)) return false; List<?> list = (List<?>) o; Iterator<?> it = list.iterator(); for (Object element : getArray()) if (!it.hasNext() || !Objects.equals(element, it.next())) return false; return !it.hasNext(); } private static int hashCodeOfRange(Object[] es, int from, int to) { int hashCode = 1; for (int i = from; i < to; i++) { Object x = es[i]; hashCode = 31 * hashCode + (x == null ? 0 : x.hashCode()); } return hashCode; } /** * Returns the hash code value for this list. * * <p>This implementation uses the definition in {@link List#hashCode}. * * @return the hash code value for this list */ public int hashCode() { Object[] es = getArray(); return hashCodeOfRange(es, 0, es.length); } /** * Returns an iterator over the elements in this list in proper sequence. * * <p>The returned iterator provides a snapshot of the state of the list * when the iterator was constructed. No synchronization is needed while * traversing the iterator. The iterator does <em>NOT</em> support the * {@code remove} method. * * @return an iterator over the elements in this list in proper sequence */ public Iterator<E> iterator() { return new COWIterator<E>(getArray(), 0); } /** * {@inheritDoc} * * <p>The returned iterator provides a snapshot of the state of the list * when the iterator was constructed. No synchronization is needed while * traversing the iterator. The iterator does <em>NOT</em> support the * {@code remove}, {@code set} or {@code add} methods. */ public ListIterator<E> listIterator() { return new COWIterator<E>(getArray(), 0); } /** * {@inheritDoc} * * <p>The returned iterator provides a snapshot of the state of the list * when the iterator was constructed. No synchronization is needed while * traversing the iterator. The iterator does <em>NOT</em> support the * {@code remove}, {@code set} or {@code add} methods. * * @throws IndexOutOfBoundsException {@inheritDoc} */ public ListIterator<E> listIterator(int index) { Object[] es = getArray(); int len = es.length; if (index < 0 || index > len) throw new IndexOutOfBoundsException(outOfBounds(index, len)); return new COWIterator<E>(es, index); } /** * Returns a {@link Spliterator} over the elements in this list. * * <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE}, * {@link Spliterator#ORDERED}, {@link Spliterator#SIZED}, and * {@link Spliterator#SUBSIZED}. * * <p>The spliterator provides a snapshot of the state of the list * when the spliterator was constructed. No synchronization is needed while * operating on the spliterator. * * @return a {@code Spliterator} over the elements in this list * @since 1.8 */ public Spliterator<E> spliterator() { return Spliterators.spliterator(getArray(), Spliterator.IMMUTABLE | Spliterator.ORDERED); } static final class COWIterator<E> implements ListIterator<E> { /** Snapshot of the array */ private final Object[] snapshot; /** Index of element to be returned by subsequent call to next. */ private int cursor; COWIterator(Object[] es, int initialCursor) { cursor = initialCursor; snapshot = es; } public boolean hasNext() { return cursor < snapshot.length; } public boolean hasPrevious() { return cursor > 0; } @SuppressWarnings("unchecked") public E next() { if (!hasNext()) throw new NoSuchElementException(); return (E) snapshot[cursor++]; } @SuppressWarnings("unchecked") public E previous() { if (!hasPrevious()) throw new NoSuchElementException(); return (E) snapshot[--cursor]; } public int nextIndex() { return cursor; } public int previousIndex() { return cursor - 1; } /** * Not supported. Always throws UnsupportedOperationException. * @throws UnsupportedOperationException always; {@code remove} * is not supported by this iterator. */ public void remove() { throw new UnsupportedOperationException(); } /** * Not supported. Always throws UnsupportedOperationException. * @throws UnsupportedOperationException always; {@code set} * is not supported by this iterator. */ public void set(E e) { throw new UnsupportedOperationException(); } /** * Not supported. Always throws UnsupportedOperationException. * @throws UnsupportedOperationException always; {@code add} * is not supported by this iterator. */ public void add(E e) { throw new UnsupportedOperationException(); } @Override public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); final int size = snapshot.length; int i = cursor; cursor = size; for (; i < size; i++) action.accept(elementAt(snapshot, i)); } } /** * Returns a view of the portion of this list between * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. * The returned list is backed by this list, so changes in the * returned list are reflected in this list. * * <p>The semantics of the list returned by this method become * undefined if the backing list (i.e., this list) is modified in * any way other than via the returned list. * * @param fromIndex low endpoint (inclusive) of the subList * @param toIndex high endpoint (exclusive) of the subList * @return a view of the specified range within this list * @throws IndexOutOfBoundsException {@inheritDoc} */ public List<E> subList(int fromIndex, int toIndex) { synchronized (lock) { Object[] es = getArray(); int len = es.length; int size = toIndex - fromIndex; if (fromIndex < 0 || toIndex > len || size < 0) throw new IndexOutOfBoundsException(); return new COWSubList(es, fromIndex, size); } } /** * Sublist for CopyOnWriteArrayList. */ private class COWSubList implements List<E>, RandomAccess { private final int offset; private int size; private Object[] expectedArray; COWSubList(Object[] es, int offset, int size) { // assert Thread.holdsLock(lock); expectedArray = es; this.offset = offset; this.size = size; } private void checkForComodification() { // assert Thread.holdsLock(lock); if (getArray() != expectedArray) throw new ConcurrentModificationException(); } private Object[] getArrayChecked() { // assert Thread.holdsLock(lock); Object[] a = getArray(); if (a != expectedArray) throw new ConcurrentModificationException(); return a; } private void rangeCheck(int index) { // assert Thread.holdsLock(lock); if (index < 0 || index >= size) throw new IndexOutOfBoundsException(outOfBounds(index, size)); } private void rangeCheckForAdd(int index) { // assert Thread.holdsLock(lock); if (index < 0 || index > size) throw new IndexOutOfBoundsException(outOfBounds(index, size)); } public Object[] toArray() { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } return Arrays.copyOfRange(es, offset, offset + size); } @SuppressWarnings("unchecked") public <T> T[] toArray(T[] a) { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } if (a.length < size) return (T[]) Arrays.copyOfRange(es, offset, offset + size, a.getClass()); else { System.arraycopy(es, offset, a, 0, size); if (a.length > size) a[size] = null; return a; } } public int indexOf(Object o) { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } int i = indexOfRange(o, es, offset, offset + size); return (i == -1) ? -1 : i - offset; } public int lastIndexOf(Object o) { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } int i = lastIndexOfRange(o, es, offset, offset + size); return (i == -1) ? -1 : i - offset; } public boolean contains(Object o) { return indexOf(o) >= 0; } public boolean containsAll(Collection<?> c) { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } for (Object o : c) if (indexOfRange(o, es, offset, offset + size) < 0) return false; return true; } public boolean isEmpty() { return size() == 0; } public String toString() { return Arrays.toString(toArray()); } public int hashCode() { final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } return hashCodeOfRange(es, offset, offset + size); } public boolean equals(Object o) { if (o == this) return true; if (!(o instanceof List)) return false; Iterator<?> it = ((List<?>) o).iterator(); final Object[] es; final int offset; final int size; synchronized (lock) { es = getArrayChecked(); offset = this.offset; size = this.size; } for (int i = offset, end = offset + size; i < end; i++) if (!it.hasNext() || !Objects.equals(es[i], it.next())) return false; return !it.hasNext(); } public E set(int index, E element) { synchronized (lock) { rangeCheck(index); checkForComodification(); E x = CopyOnWriteArrayList.this.set(offset + index, element); expectedArray = getArray(); return x; } } public E get(int index) { synchronized (lock) { rangeCheck(index); checkForComodification(); return CopyOnWriteArrayList.this.get(offset + index); } } public int size() { synchronized (lock) { checkForComodification(); return size; } } public boolean add(E element) { synchronized (lock) { checkForComodification(); CopyOnWriteArrayList.this.add(offset + size, element); expectedArray = getArray(); size++; } return true; } public void add(int index, E element) { synchronized (lock) { checkForComodification(); rangeCheckForAdd(index); CopyOnWriteArrayList.this.add(offset + index, element); expectedArray = getArray(); size++; } } public boolean addAll(Collection<? extends E> c) { synchronized (lock) { final Object[] oldArray = getArrayChecked(); boolean modified = CopyOnWriteArrayList.this.addAll(offset + size, c); size += (expectedArray = getArray()).length - oldArray.length; return modified; } } public boolean addAll(int index, Collection<? extends E> c) { synchronized (lock) { rangeCheckForAdd(index); final Object[] oldArray = getArrayChecked(); boolean modified = CopyOnWriteArrayList.this.addAll(offset + index, c); size += (expectedArray = getArray()).length - oldArray.length; return modified; } } public void clear() { synchronized (lock) { checkForComodification(); removeRange(offset, offset + size); expectedArray = getArray(); size = 0; } } public E remove(int index) { synchronized (lock) { rangeCheck(index); checkForComodification(); E result = CopyOnWriteArrayList.this.remove(offset + index); expectedArray = getArray(); size--; return result; } } public boolean remove(Object o) { synchronized (lock) { checkForComodification(); int index = indexOf(o); if (index == -1) return false; remove(index); return true; } } public Iterator<E> iterator() { return listIterator(0); } public ListIterator<E> listIterator() { return listIterator(0); } public ListIterator<E> listIterator(int index) { synchronized (lock) { checkForComodification(); rangeCheckForAdd(index); return new COWSubListIterator<E>(CopyOnWriteArrayList.this, index, offset, size); } } public List<E> subList(int fromIndex, int toIndex) { synchronized (lock) { checkForComodification(); if (fromIndex < 0 || toIndex > size || fromIndex > toIndex) throw new IndexOutOfBoundsException(); return new COWSubList(expectedArray, fromIndex + offset, toIndex - fromIndex); } } public void forEach(Consumer<? super E> action) { Objects.requireNonNull(action); int i, end; final Object[] es; synchronized (lock) { es = getArrayChecked(); i = offset; end = i + size; } for (; i < end; i++) action.accept(elementAt(es, i)); } public void replaceAll(UnaryOperator<E> operator) { synchronized (lock) { checkForComodification(); replaceAllRange(operator, offset, offset + size); expectedArray = getArray(); } } public void sort(Comparator<? super E> c) { synchronized (lock) { checkForComodification(); sortRange(c, offset, offset + size); expectedArray = getArray(); } } public boolean removeAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> c.contains(e)); } public boolean retainAll(Collection<?> c) { Objects.requireNonNull(c); return bulkRemove(e -> !c.contains(e)); } public boolean removeIf(Predicate<? super E> filter) { Objects.requireNonNull(filter); return bulkRemove(filter); } private boolean bulkRemove(Predicate<? super E> filter) { synchronized (lock) { final Object[] oldArray = getArrayChecked(); boolean modified = CopyOnWriteArrayList.this.bulkRemove(filter, offset, offset + size); size += (expectedArray = getArray()).length - oldArray.length; return modified; } } public Spliterator<E> spliterator() { synchronized (lock) { return Spliterators.spliterator(getArrayChecked(), offset, offset + size, Spliterator.IMMUTABLE | Spliterator.ORDERED); } } } private static class COWSubListIterator<E> implements ListIterator<E> { private final ListIterator<E> it; private final int offset; private final int size; COWSubListIterator(List<E> l, int index, int offset, int size) { this.offset = offset; this.size = size; it = l.listIterator(index + offset); } public boolean hasNext() { return nextIndex() < size; } public E next() { if (hasNext()) return it.next(); else throw new NoSuchElementException(); } public boolean hasPrevious() { return previousIndex() >= 0; } public E previous() { if (hasPrevious()) return it.previous(); else throw new NoSuchElementException(); } public int nextIndex() { return it.nextIndex() - offset; } public int previousIndex() { return it.previousIndex() - offset; } public void remove() { throw new UnsupportedOperationException(); } public void set(E e) { throw new UnsupportedOperationException(); } public void add(E e) { throw new UnsupportedOperationException(); } @Override @SuppressWarnings("unchecked") public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); while (hasNext()) { action.accept(it.next()); } } } /** Initializes the lock; for use when deserializing or cloning. */ private void resetLock() { Field lockField = java.security.AccessController .doPrivileged((java.security.PrivilegedAction<Field>) () -> { try { Field f = CopyOnWriteArrayList.class.getDeclaredField("lock"); f.setAccessible(true); return f; } catch (ReflectiveOperationException e) { throw new Error(e); } }); try { lockField.set(this, new Object()); } catch (IllegalAccessException e) { throw new Error(e); } } }