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/* * 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.util.function.Consumer; /** * This class provides a skeletal implementation of the {@link List} * interface to minimize the effort required to implement this interface * backed by a "random access" data store (such as an array). For sequential * access data (such as a linked list), {@link AbstractSequentialList} should * be used in preference to this class. * * <p>To implement an unmodifiable list, the programmer needs only to extend * this class and provide implementations for the {@link #get(int)} and * {@link List#size() size()} methods. * * <p>To implement a modifiable list, the programmer must additionally * override the {@link #set(int, Object) set(int, E)} method (which otherwise * throws an {@code UnsupportedOperationException}). If the list is * variable-size the programmer must additionally override the * {@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods. * * <p>The programmer should generally provide a void (no argument) and collection * constructor, as per the recommendation in the {@link Collection} interface * specification. * * <p>Unlike the other abstract collection implementations, the programmer does * <i>not</i> have to provide an iterator implementation; the iterator and * list iterator are implemented by this class, on top of the "random access" * methods: * {@link #get(int)}, * {@link #set(int, Object) set(int, E)}, * {@link #add(int, Object) add(int, E)} and * {@link #remove(int)}. * * <p>The documentation for each non-abstract method in this class describes its * implementation in detail. Each of these methods may be overridden if the * collection being implemented admits a more efficient implementation. * * <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 * @since 1.2 */ public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> { /** * Sole constructor. (For invocation by subclass constructors, typically * implicit.) */ protected AbstractList() { } /** * Appends the specified element to the end of this list (optional * operation). * * <p>Lists that support this operation may place limitations on what * elements may be added to this list. In particular, some * lists will refuse to add null elements, and others will impose * restrictions on the type of elements that may be added. List * classes should clearly specify in their documentation any restrictions * on what elements may be added. * * @implSpec * This implementation calls {@code add(size(), e)}. * * <p>Note that this implementation throws an * {@code UnsupportedOperationException} unless * {@link #add(int, Object) add(int, E)} is overridden. * * @param e element to be appended to this list * @return {@code true} (as specified by {@link Collection#add}) * @throws UnsupportedOperationException if the {@code add} operation * is not supported by this list * @throws ClassCastException if the class of the specified element * prevents it from being added to this list * @throws NullPointerException if the specified element is null and this * list does not permit null elements * @throws IllegalArgumentException if some property of this element * prevents it from being added to this list */ public boolean add(E e) { add(size(), e); return true; } /** * {@inheritDoc} * * @throws IndexOutOfBoundsException {@inheritDoc} */ public abstract E get(int index); /** * {@inheritDoc} * * @implSpec * This implementation always throws an * {@code UnsupportedOperationException}. * * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} * @throws IndexOutOfBoundsException {@inheritDoc} */ public E set(int index, E element) { throw new UnsupportedOperationException(); } /** * {@inheritDoc} * * @implSpec * This implementation always throws an * {@code UnsupportedOperationException}. * * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} * @throws IndexOutOfBoundsException {@inheritDoc} */ public void add(int index, E element) { throw new UnsupportedOperationException(); } /** * {@inheritDoc} * * @implSpec * This implementation always throws an * {@code UnsupportedOperationException}. * * @throws UnsupportedOperationException {@inheritDoc} * @throws IndexOutOfBoundsException {@inheritDoc} */ public E remove(int index) { throw new UnsupportedOperationException(); } // Search Operations /** * {@inheritDoc} * * @implSpec * This implementation first gets a list iterator (with * {@code listIterator()}). Then, it iterates over the list until the * specified element is found or the end of the list is reached. * * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public int indexOf(Object o) { ListIterator<E> it = listIterator(); if (o == null) { while (it.hasNext()) if (it.next() == null) return it.previousIndex(); } else { while (it.hasNext()) if (o.equals(it.next())) return it.previousIndex(); } return -1; } /** * {@inheritDoc} * * @implSpec * This implementation first gets a list iterator that points to the end * of the list (with {@code listIterator(size())}). Then, it iterates * backwards over the list until the specified element is found, or the * beginning of the list is reached. * * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public int lastIndexOf(Object o) { ListIterator<E> it = listIterator(size()); if (o == null) { while (it.hasPrevious()) if (it.previous() == null) return it.nextIndex(); } else { while (it.hasPrevious()) if (o.equals(it.previous())) return it.nextIndex(); } return -1; } // Bulk Operations /** * Removes all of the elements from this list (optional operation). * The list will be empty after this call returns. * * @implSpec * This implementation calls {@code removeRange(0, size())}. * * <p>Note that this implementation throws an * {@code UnsupportedOperationException} unless {@code remove(int * index)} or {@code removeRange(int fromIndex, int toIndex)} is * overridden. * * @throws UnsupportedOperationException if the {@code clear} operation * is not supported by this list */ public void clear() { removeRange(0, size()); } /** * {@inheritDoc} * * @implSpec * This implementation gets an iterator over the specified collection * and iterates over it, inserting the elements obtained from the * iterator into this list at the appropriate position, one at a time, * using {@code add(int, E)}. * Many implementations will override this method for efficiency. * * <p>Note that this implementation throws an * {@code UnsupportedOperationException} unless * {@link #add(int, Object) add(int, E)} is overridden. * * @throws UnsupportedOperationException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException {@inheritDoc} * @throws IllegalArgumentException {@inheritDoc} * @throws IndexOutOfBoundsException {@inheritDoc} */ public boolean addAll(int index, Collection<? extends E> c) { rangeCheckForAdd(index); boolean modified = false; for (E e : c) { add(index++, e); modified = true; } return modified; } // Iterators /** * Returns an iterator over the elements in this list in proper sequence. * * @implSpec * This implementation returns a straightforward implementation of the * iterator interface, relying on the backing list's {@code size()}, * {@code get(int)}, and {@code remove(int)} methods. * * <p>Note that the iterator returned by this method will throw an * {@link UnsupportedOperationException} in response to its * {@code remove} method unless the list's {@code remove(int)} method is * overridden. * * <p>This implementation can be made to throw runtime exceptions in the * face of concurrent modification, as described in the specification * for the (protected) {@link #modCount} field. * * @return an iterator over the elements in this list in proper sequence */ public Iterator<E> iterator() { return new Itr(); } /** * {@inheritDoc} * * @implSpec * This implementation returns {@code listIterator(0)}. * * @see #listIterator(int) */ public ListIterator<E> listIterator() { return listIterator(0); } /** * {@inheritDoc} * * @implSpec * This implementation returns a straightforward implementation of the * {@code ListIterator} interface that extends the implementation of the * {@code Iterator} interface returned by the {@code iterator()} method. * The {@code ListIterator} implementation relies on the backing list's * {@code get(int)}, {@code set(int, E)}, {@code add(int, E)} * and {@code remove(int)} methods. * * <p>Note that the list iterator returned by this implementation will * throw an {@link UnsupportedOperationException} in response to its * {@code remove}, {@code set} and {@code add} methods unless the * list's {@code remove(int)}, {@code set(int, E)}, and * {@code add(int, E)} methods are overridden. * * <p>This implementation can be made to throw runtime exceptions in the * face of concurrent modification, as described in the specification for * the (protected) {@link #modCount} field. * * @throws IndexOutOfBoundsException {@inheritDoc} */ public ListIterator<E> listIterator(final int index) { rangeCheckForAdd(index); return new ListItr(index); } private class Itr implements Iterator<E> { /** * Index of element to be returned by subsequent call to next. */ int cursor = 0; /** * Index of element returned by most recent call to next or * previous. Reset to -1 if this element is deleted by a call * to remove. */ int lastRet = -1; /** * The modCount value that the iterator believes that the backing * List should have. If this expectation is violated, the iterator * has detected concurrent modification. */ int expectedModCount = modCount; public boolean hasNext() { return cursor != size(); } public E next() { checkForComodification(); try { int i = cursor; E next = get(i); lastRet = i; cursor = i + 1; return next; } catch (IndexOutOfBoundsException e) { checkForComodification(); throw new NoSuchElementException(); } } public void remove() { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { AbstractList.this.remove(lastRet); if (lastRet < cursor) cursor--; lastRet = -1; expectedModCount = modCount; } catch (IndexOutOfBoundsException e) { throw new ConcurrentModificationException(); } } final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); } } private class ListItr extends Itr implements ListIterator<E> { ListItr(int index) { cursor = index; } public boolean hasPrevious() { return cursor != 0; } public E previous() { checkForComodification(); try { int i = cursor - 1; E previous = get(i); lastRet = cursor = i; return previous; } catch (IndexOutOfBoundsException e) { checkForComodification(); throw new NoSuchElementException(); } } public int nextIndex() { return cursor; } public int previousIndex() { return cursor - 1; } public void set(E e) { if (lastRet < 0) throw new IllegalStateException(); checkForComodification(); try { AbstractList.this.set(lastRet, e); expectedModCount = modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } public void add(E e) { checkForComodification(); try { int i = cursor; AbstractList.this.add(i, e); lastRet = -1; cursor = i + 1; expectedModCount = modCount; } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } } /** * {@inheritDoc} * * @implSpec * This implementation returns a list that subclasses * {@code AbstractList}. The subclass stores, in private fields, the * size of the subList (which can change over its lifetime), and the * expected {@code modCount} value of the backing list. There are two * variants of the subclass, one of which implements {@code RandomAccess}. * If this list implements {@code RandomAccess} the returned list will * be an instance of the subclass that implements {@code RandomAccess}. * * <p>The subclass's {@code set(int, E)}, {@code get(int)}, * {@code add(int, E)}, {@code remove(int)}, {@code addAll(int, * Collection)} and {@code removeRange(int, int)} methods all * delegate to the corresponding methods on the backing abstract list, * after bounds-checking the index and adjusting for the offset. The * {@code addAll(Collection c)} method merely returns {@code addAll(size, * c)}. * * <p>The {@code listIterator(int)} method returns a "wrapper object" * over a list iterator on the backing list, which is created with the * corresponding method on the backing list. The {@code iterator} method * merely returns {@code listIterator()}, and the {@code size} method * merely returns the subclass's {@code size} field. * * <p>All methods first check to see if the actual {@code modCount} of * the backing list is equal to its expected value, and throw a * {@code ConcurrentModificationException} if it is not. * * @throws IndexOutOfBoundsException if an endpoint index value is out of range * {@code (fromIndex < 0 || toIndex > size)} * @throws IllegalArgumentException if the endpoint indices are out of order * {@code (fromIndex > toIndex)} */ public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size()); return (this instanceof RandomAccess ? new RandomAccessSubList<>(this, fromIndex, toIndex) : new SubList<>(this, fromIndex, toIndex)); } static void subListRangeCheck(int fromIndex, int toIndex, int size) { if (fromIndex < 0) throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); if (toIndex > size) throw new IndexOutOfBoundsException("toIndex = " + toIndex); if (fromIndex > toIndex) throw new IllegalArgumentException("fromIndex(" + fromIndex + ") > toIndex(" + toIndex + ")"); } // Comparison and hashing /** * Compares the specified object with this list for equality. Returns * {@code true} if and only if the specified object is also a list, both * lists have the same size, and all corresponding pairs of elements in * the two lists are <i>equal</i>. (Two elements {@code e1} and * {@code e2} are <i>equal</i> if {@code (e1==null ? e2==null : * e1.equals(e2))}.) In other words, two lists are defined to be * equal if they contain the same elements in the same order. * * @implSpec * This implementation first checks if the specified object is this * list. If so, it returns {@code true}; if not, it checks if the * specified object is a list. If not, it returns {@code false}; if so, * it iterates over both lists, comparing corresponding pairs of elements. * If any comparison returns {@code false}, this method returns * {@code false}. If either iterator runs out of elements before the * other it returns {@code false} (as the lists are of unequal length); * otherwise it returns {@code true} when the iterations complete. * * @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; ListIterator<E> e1 = listIterator(); ListIterator<?> e2 = ((List<?>) o).listIterator(); while (e1.hasNext() && e2.hasNext()) { E o1 = e1.next(); Object o2 = e2.next(); if (!(o1 == null ? o2 == null : o1.equals(o2))) return false; } return !(e1.hasNext() || e2.hasNext()); } /** * Returns the hash code value for this list. * * @implSpec * This implementation uses exactly the code that is used to define the * list hash function in the documentation for the {@link List#hashCode} * method. * * @return the hash code value for this list */ public int hashCode() { int hashCode = 1; for (E e : this) hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode()); return hashCode; } /** * 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.) * * <p>This method is called by the {@code clear} operation on this list * and its subLists. Overriding this method to take advantage of * the internals of the list implementation can <i>substantially</i> * improve the performance of the {@code clear} operation on this list * and its subLists. * * @implSpec * This implementation gets a list iterator positioned before * {@code fromIndex}, and repeatedly calls {@code ListIterator.next} * followed by {@code ListIterator.remove} until the entire range has * been removed. <b>Note: if {@code ListIterator.remove} requires linear * time, this implementation requires quadratic time.</b> * * @param fromIndex index of first element to be removed * @param toIndex index after last element to be removed */ protected void removeRange(int fromIndex, int toIndex) { ListIterator<E> it = listIterator(fromIndex); for (int i = 0, n = toIndex - fromIndex; i < n; i++) { it.next(); it.remove(); } } /** * The number of times this list has been <i>structurally modified</i>. * Structural modifications are those that change the size of the * list, or otherwise perturb it in such a fashion that iterations in * progress may yield incorrect results. * * <p>This field is used by the iterator and list iterator implementation * returned by the {@code iterator} and {@code listIterator} methods. * If the value of this field changes unexpectedly, the iterator (or list * iterator) will throw a {@code ConcurrentModificationException} in * response to the {@code next}, {@code remove}, {@code previous}, * {@code set} or {@code add} operations. This provides * <i>fail-fast</i> behavior, rather than non-deterministic behavior in * the face of concurrent modification during iteration. * * <p><b>Use of this field by subclasses is optional.</b> If a subclass * wishes to provide fail-fast iterators (and list iterators), then it * merely has to increment this field in its {@code add(int, E)} and * {@code remove(int)} methods (and any other methods that it overrides * that result in structural modifications to the list). A single call to * {@code add(int, E)} or {@code remove(int)} must add no more than * one to this field, or the iterators (and list iterators) will throw * bogus {@code ConcurrentModificationExceptions}. If an implementation * does not wish to provide fail-fast iterators, this field may be * ignored. */ protected transient int modCount = 0; private void rangeCheckForAdd(int index) { if (index < 0 || index > size()) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private String outOfBoundsMsg(int index) { return "Index: " + index + ", Size: " + size(); } /** * An index-based split-by-two, lazily initialized Spliterator covering * a List that access elements via {@link List#get}. * * If access results in an IndexOutOfBoundsException then a * ConcurrentModificationException is thrown instead (since the list has * been structurally modified while traversing). * * If the List is an instance of AbstractList then concurrent modification * checking is performed using the AbstractList's modCount field. */ static final class RandomAccessSpliterator<E> implements Spliterator<E> { private final List<E> list; private int index; // current index, modified on advance/split private int fence; // -1 until used; then one past last index // The following fields are valid if covering an AbstractList private final AbstractList<E> alist; private int expectedModCount; // initialized when fence set RandomAccessSpliterator(List<E> list) { assert list instanceof RandomAccess; this.list = list; this.index = 0; this.fence = -1; this.alist = list instanceof AbstractList ? (AbstractList<E>) list : null; this.expectedModCount = alist != null ? alist.modCount : 0; } /** Create new spliterator covering the given range */ private RandomAccessSpliterator(RandomAccessSpliterator<E> parent, int origin, int fence) { this.list = parent.list; this.index = origin; this.fence = fence; this.alist = parent.alist; this.expectedModCount = parent.expectedModCount; } private int getFence() { // initialize fence to size on first use int hi; List<E> lst = list; if ((hi = fence) < 0) { if (alist != null) { expectedModCount = alist.modCount; } hi = fence = lst.size(); } return hi; } public Spliterator<E> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid) ? null : // divide range in half unless too small new RandomAccessSpliterator<>(this, lo, index = mid); } public boolean tryAdvance(Consumer<? super E> action) { if (action == null) throw new NullPointerException(); int hi = getFence(), i = index; if (i < hi) { index = i + 1; action.accept(get(list, i)); checkAbstractListModCount(alist, expectedModCount); return true; } return false; } public void forEachRemaining(Consumer<? super E> action) { Objects.requireNonNull(action); List<E> lst = list; int hi = getFence(); int i = index; index = hi; for (; i < hi; i++) { action.accept(get(lst, i)); } checkAbstractListModCount(alist, expectedModCount); } public long estimateSize() { return (long) (getFence() - index); } public int characteristics() { return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED; } private static <E> E get(List<E> list, int i) { try { return list.get(i); } catch (IndexOutOfBoundsException ex) { throw new ConcurrentModificationException(); } } static void checkAbstractListModCount(AbstractList<?> alist, int expectedModCount) { if (alist != null && alist.modCount != expectedModCount) { throw new ConcurrentModificationException(); } } } private static class SubList<E> extends AbstractList<E> { private final AbstractList<E> root; private final SubList<E> parent; private final int offset; protected int size; /** * Constructs a sublist of an arbitrary AbstractList, which is * not a SubList itself. */ public SubList(AbstractList<E> root, int fromIndex, int toIndex) { this.root = root; this.parent = null; this.offset = fromIndex; this.size = toIndex - fromIndex; this.modCount = root.modCount; } /** * Constructs a sublist of another SubList. */ protected SubList(SubList<E> parent, int fromIndex, int toIndex) { this.root = parent.root; this.parent = parent; this.offset = parent.offset + fromIndex; this.size = toIndex - fromIndex; this.modCount = root.modCount; } public E set(int index, E element) { Objects.checkIndex(index, size); checkForComodification(); return root.set(offset + index, element); } public E get(int index) { Objects.checkIndex(index, size); checkForComodification(); return root.get(offset + index); } public int size() { checkForComodification(); return size; } public void add(int index, E element) { rangeCheckForAdd(index); checkForComodification(); root.add(offset + index, element); updateSizeAndModCount(1); } public E remove(int index) { Objects.checkIndex(index, size); checkForComodification(); E result = root.remove(offset + index); updateSizeAndModCount(-1); return result; } protected void removeRange(int fromIndex, int toIndex) { checkForComodification(); root.removeRange(offset + fromIndex, offset + toIndex); updateSizeAndModCount(fromIndex - toIndex); } public boolean addAll(Collection<? extends E> c) { return addAll(size, c); } public boolean addAll(int index, Collection<? extends E> c) { rangeCheckForAdd(index); int cSize = c.size(); if (cSize == 0) return false; checkForComodification(); root.addAll(offset + index, c); updateSizeAndModCount(cSize); return true; } public Iterator<E> iterator() { return listIterator(); } public ListIterator<E> listIterator(int index) { checkForComodification(); rangeCheckForAdd(index); return new ListIterator<E>() { private final ListIterator<E> i = root.listIterator(offset + index); public boolean hasNext() { return nextIndex() < size; } public E next() { if (hasNext()) return i.next(); else throw new NoSuchElementException(); } public boolean hasPrevious() { return previousIndex() >= 0; } public E previous() { if (hasPrevious()) return i.previous(); else throw new NoSuchElementException(); } public int nextIndex() { return i.nextIndex() - offset; } public int previousIndex() { return i.previousIndex() - offset; } public void remove() { i.remove(); updateSizeAndModCount(-1); } public void set(E e) { i.set(e); } public void add(E e) { i.add(e); updateSizeAndModCount(1); } }; } public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size); return new SubList<>(this, fromIndex, toIndex); } private void rangeCheckForAdd(int index) { if (index < 0 || index > size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); } private String outOfBoundsMsg(int index) { return "Index: " + index + ", Size: " + size; } private void checkForComodification() { if (root.modCount != this.modCount) throw new ConcurrentModificationException(); } private void updateSizeAndModCount(int sizeChange) { SubList<E> slist = this; do { slist.size += sizeChange; slist.modCount = root.modCount; slist = slist.parent; } while (slist != null); } } private static class RandomAccessSubList<E> extends SubList<E> implements RandomAccess { /** * Constructs a sublist of an arbitrary AbstractList, which is * not a RandomAccessSubList itself. */ RandomAccessSubList(AbstractList<E> root, int fromIndex, int toIndex) { super(root, fromIndex, toIndex); } /** * Constructs a sublist of another RandomAccessSubList. */ RandomAccessSubList(RandomAccessSubList<E> parent, int fromIndex, int toIndex) { super(parent, fromIndex, toIndex); } public List<E> subList(int fromIndex, int toIndex) { subListRangeCheck(fromIndex, toIndex, size); return new RandomAccessSubList<>(this, fromIndex, toIndex); } } }