/* * 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.util.AbstractList; 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; // BEGIN android-note // removed link to collections framework docs // fixed framework docs link to "Collection#optional" // END android-note /** * 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. * *

This is ordinarily too costly, but may be more 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}. * *

All elements are permitted, including {@code null}. * *

Memory consistency effects: As with other concurrent * collections, actions in a thread prior to placing an object into a * {@code CopyOnWriteArrayList} * happen-before * actions subsequent to the access or removal of that element from * the {@code CopyOnWriteArrayList} in another thread. * * @since 1.5 * @author Doug Lea * @param the type of elements held in this list */ public class CopyOnWriteArrayList implements List, 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. */ // Android-changed: renamed array -> elements for backwards compatibility b/33916927 private transient volatile Object[] elements; /** * Gets the array. Non-private so as to also be accessible * from CopyOnWriteArraySet class. */ final Object[] getArray() { return elements; } /** * Sets the array. */ final void setArray(Object[] a) { elements = 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 c) { Object[] elements; if (c.getClass() == CopyOnWriteArrayList.class) elements = ((CopyOnWriteArrayList)c).getArray(); else { elements = c.toArray(); // defend against c.toArray (incorrectly) not returning Object[] // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652) if (elements.getClass() != Object[].class) elements = Arrays.copyOf(elements, elements.length, Object[].class); } setArray(elements); } /** * 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 elements the array * @param index first index to search * @param fence one past last index to search * @return index of element, or -1 if absent */ private static int indexOf(Object o, Object[] elements, int index, int fence) { if (o == null) { for (int i = index; i < fence; i++) if (elements[i] == null) return i; } else { for (int i = index; i < fence; i++) if (o.equals(elements[i])) return i; } return -1; } /** * static version of lastIndexOf. * @param o element to search for * @param elements the array * @param index first index to search * @return index of element, or -1 if absent */ private static int lastIndexOf(Object o, Object[] elements, int index) { if (o == null) { for (int i = index; i >= 0; i--) if (elements[i] == null) return i; } else { for (int i = index; i >= 0; i--) if (o.equals(elements[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) { Object[] elements = getArray(); return indexOf(o, elements, 0, elements.length) >= 0; } /** * {@inheritDoc} */ public int indexOf(Object o) { Object[] elements = getArray(); return indexOf(o, elements, 0, elements.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[] elements = getArray(); return indexOf(e, elements, index, elements.length); } /** * {@inheritDoc} */ public int lastIndexOf(Object o) { Object[] elements = getArray(); return lastIndexOf(o, elements, elements.length - 1); } /** * 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[] elements = getArray(); return lastIndexOf(e, elements, index); } /** * 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 clone = (CopyOnWriteArrayList) super.clone(); clone.resetLock(); 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). * *

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. * *

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() { Object[] elements = getArray(); return Arrays.copyOf(elements, elements.length); } /** * 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. * *

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 only if the caller knows that this list does not contain * any null elements.) * *

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. * *

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}: * *

 {@code String[] y = x.toArray(new String[0]);}
* * 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[] toArray(T[] a) { Object[] elements = getArray(); int len = elements.length; if (a.length < len) return (T[]) Arrays.copyOf(elements, len, a.getClass()); else { System.arraycopy(elements, 0, a, 0, len); if (a.length > len) a[len] = null; return a; } } // Positional Access Operations @SuppressWarnings("unchecked") private E get(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 get(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[] elements = getArray(); E oldValue = get(elements, index); if (oldValue != element) { int len = elements.length; Object[] newElements = Arrays.copyOf(elements, len); newElements[index] = element; setArray(newElements); } else { // Not quite a no-op; ensures volatile write semantics setArray(elements); } 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[] elements = getArray(); int len = elements.length; Object[] newElements = Arrays.copyOf(elements, len + 1); newElements[len] = e; setArray(newElements); 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[] elements = getArray(); int len = elements.length; if (index > len || index < 0) throw new IndexOutOfBoundsException(outOfBounds(index, len)); Object[] newElements; int numMoved = len - index; if (numMoved == 0) newElements = Arrays.copyOf(elements, len + 1); else { newElements = new Object[len + 1]; System.arraycopy(elements, 0, newElements, 0, index); System.arraycopy(elements, 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[] elements = getArray(); int len = elements.length; E oldValue = get(elements, index); int numMoved = len - index - 1; if (numMoved == 0) setArray(Arrays.copyOf(elements, len - 1)); else { Object[] newElements = new Object[len - 1]; System.arraycopy(elements, 0, newElements, 0, index); System.arraycopy(elements, 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 = indexOf(o, snapshot, 0, snapshot.length); return (index < 0) ? false : 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 = indexOf(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[] elements = getArray(); int len = elements.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(elements, newlen)); else { Object[] newElements = new Object[newlen]; System.arraycopy(elements, 0, newElements, 0, fromIndex); System.arraycopy(elements, 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 indexOf(e, snapshot, 0, snapshot.length) >= 0 ? false : 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 (indexOf(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[] elements = getArray(); int len = elements.length; for (Object e : c) { if (indexOf(e, elements, 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 * (optional) * @throws NullPointerException if this list contains a null element and the * specified collection does not permit null elements * (optional), * or if the specified collection is null * @see #remove(Object) */ public boolean removeAll(Collection c) { if (c == null) throw new NullPointerException(); synchronized (lock) { Object[] elements = getArray(); int len = elements.length; if (len != 0) { // temp array holds those elements we know we want to keep int newlen = 0; Object[] temp = new Object[len]; for (int i = 0; i < len; ++i) { Object element = elements[i]; if (!c.contains(element)) temp[newlen++] = element; } if (newlen != len) { setArray(Arrays.copyOf(temp, newlen)); return true; } } return false; } } /** * 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 * (optional) * @throws NullPointerException if this list contains a null element and the * specified collection does not permit null elements * (optional), * or if the specified collection is null * @see #remove(Object) */ public boolean retainAll(Collection c) { if (c == null) throw new NullPointerException(); synchronized (lock) { Object[] elements = getArray(); int len = elements.length; if (len != 0) { // temp array holds those elements we know we want to keep int newlen = 0; Object[] temp = new Object[len]; for (int i = 0; i < len; ++i) { Object element = elements[i]; if (c.contains(element)) temp[newlen++] = element; } if (newlen != len) { setArray(Arrays.copyOf(temp, newlen)); return true; } } return false; } } /** * 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 c) { Object[] cs = c.toArray(); if (cs.length == 0) return 0; synchronized (lock) { Object[] elements = getArray(); int len = elements.length; int added = 0; // uniquify and compact elements in cs for (int i = 0; i < cs.length; ++i) { Object e = cs[i]; if (indexOf(e, elements, 0, len) < 0 && indexOf(e, cs, 0, added) < 0) cs[added++] = e; } if (added > 0) { Object[] newElements = Arrays.copyOf(elements, 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 c) { Object[] cs = (c.getClass() == CopyOnWriteArrayList.class) ? ((CopyOnWriteArrayList)c).getArray() : c.toArray(); if (cs.length == 0) return false; synchronized (lock) { Object[] elements = getArray(); int len = elements.length; if (len == 0 && cs.getClass() == Object[].class) setArray(cs); else { Object[] newElements = Arrays.copyOf(elements, 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 c) { Object[] cs = c.toArray(); synchronized (lock) { Object[] elements = getArray(); int len = elements.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(elements, len + cs.length); else { newElements = new Object[len + cs.length]; System.arraycopy(elements, 0, newElements, 0, index); System.arraycopy(elements, index, newElements, index + cs.length, numMoved); } System.arraycopy(cs, 0, newElements, index, cs.length); setArray(newElements); return true; } } public void forEach(Consumer action) { if (action == null) throw new NullPointerException(); for (Object x : getArray()) { @SuppressWarnings("unchecked") E e = (E) x; action.accept(e); } } public boolean removeIf(Predicate filter) { if (filter == null) throw new NullPointerException(); synchronized (lock) { final Object[] elements = getArray(); final int len = elements.length; int i; for (i = 0; i < len; i++) { @SuppressWarnings("unchecked") E e = (E) elements[i]; if (filter.test(e)) { int newlen = i; final Object[] newElements = new Object[len - 1]; System.arraycopy(elements, 0, newElements, 0, newlen); for (i++; i < len; i++) { @SuppressWarnings("unchecked") E x = (E) elements[i]; if (!filter.test(x)) newElements[newlen++] = x; } setArray((newlen == len - 1) ? newElements // one match => one copy : Arrays.copyOf(newElements, newlen)); return true; } } return false; // zero matches => zero copies } } public void replaceAll(UnaryOperator operator) { if (operator == null) throw new NullPointerException(); synchronized (lock) { Object[] elements = getArray(); int len = elements.length; Object[] newElements = Arrays.copyOf(elements, len); for (int i = 0; i < len; ++i) { @SuppressWarnings("unchecked") E e = (E) elements[i]; newElements[i] = operator.apply(e); } setArray(newElements); } } public void sort(Comparator c) { synchronized (lock) { Object[] elements = getArray(); Object[] newElements = Arrays.copyOf(elements, elements.length); @SuppressWarnings("unchecked") E[] es = (E[])newElements; Arrays.sort(es, c); setArray(newElements); } } /** * 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[] elements = getArray(); // Write out array length s.writeInt(elements.length); // Write out all elements in the proper order. for (Object element : elements) 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(); Object[] elements = new Object[len]; // Read in all elements in the proper order. for (int i = 0; i < len; i++) elements[i] = s.readObject(); setArray(elements); } /** * 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 equal. * Two elements {@code e1} and {@code e2} are considered * equal 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(); Object[] elements = getArray(); for (int i = 0, len = elements.length; i < len; i++) if (!it.hasNext() || !Objects.equals(elements[i], it.next())) return false; if (it.hasNext()) return false; return true; } /** * Returns the hash code value for this list. * *

This implementation uses the definition in {@link List#hashCode}. * * @return the hash code value for this list */ public int hashCode() { int hashCode = 1; for (Object x : getArray()) hashCode = 31 * hashCode + (x == null ? 0 : x.hashCode()); return hashCode; } /** * Returns an iterator over the elements in this list in proper sequence. * *

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 NOT support the * {@code remove} method. * * @return an iterator over the elements in this list in proper sequence */ public Iterator iterator() { return new COWIterator(getArray(), 0); } /** * {@inheritDoc} * *

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 NOT support the * {@code remove}, {@code set} or {@code add} methods. */ public ListIterator listIterator() { return new COWIterator(getArray(), 0); } /** * {@inheritDoc} * *

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 NOT support the * {@code remove}, {@code set} or {@code add} methods. * * @throws IndexOutOfBoundsException {@inheritDoc} */ public ListIterator listIterator(int index) { Object[] elements = getArray(); int len = elements.length; if (index < 0 || index > len) throw new IndexOutOfBoundsException(outOfBounds(index, len)); return new COWIterator(elements, index); } /** * Returns a {@link Spliterator} over the elements in this list. * *

The {@code Spliterator} reports {@link Spliterator#IMMUTABLE}, * {@link Spliterator#ORDERED}, {@link Spliterator#SIZED}, and * {@link Spliterator#SUBSIZED}. * *

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 spliterator() { return Spliterators.spliterator (getArray(), Spliterator.IMMUTABLE | Spliterator.ORDERED); } static final class COWIterator implements ListIterator { /** Snapshot of the array */ private final Object[] snapshot; /** Index of element to be returned by subsequent call to next. */ private int cursor; COWIterator(Object[] elements, int initialCursor) { cursor = initialCursor; snapshot = elements; } 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 @SuppressWarnings("unchecked") public void forEachRemaining(Consumer action) { Objects.requireNonNull(action); final int size = snapshot.length; for (int i = cursor; i < size; i++) { action.accept((E) snapshot[i]); } cursor = size; } } /** * 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. * *

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 subList(int fromIndex, int toIndex) { synchronized (lock) { Object[] elements = getArray(); int len = elements.length; if (fromIndex < 0 || toIndex > len || fromIndex > toIndex) throw new IndexOutOfBoundsException(); return new COWSubList(this, fromIndex, toIndex); } } /** * Sublist for CopyOnWriteArrayList. * This class extends AbstractList merely for convenience, to * avoid having to define addAll, etc. This doesn't hurt, but * is wasteful. This class does not need or use modCount * mechanics in AbstractList, but does need to check for * concurrent modification using similar mechanics. On each * operation, the array that we expect the backing list to use * is checked and updated. Since we do this for all of the * base operations invoked by those defined in AbstractList, * all is well. While inefficient, this is not worth * improving. The kinds of list operations inherited from * AbstractList are already so slow on COW sublists that * adding a bit more space/time doesn't seem even noticeable. */ private static class COWSubList extends AbstractList implements RandomAccess { private final CopyOnWriteArrayList l; private final int offset; private int size; private Object[] expectedArray; // only call this holding l's lock COWSubList(CopyOnWriteArrayList list, int fromIndex, int toIndex) { // assert Thread.holdsLock(list.lock); l = list; expectedArray = l.getArray(); offset = fromIndex; size = toIndex - fromIndex; } // only call this holding l's lock private void checkForComodification() { // assert Thread.holdsLock(l.lock); if (l.getArray() != expectedArray) throw new ConcurrentModificationException(); } // only call this holding l's lock private void rangeCheck(int index) { // assert Thread.holdsLock(l.lock); if (index < 0 || index >= size) throw new IndexOutOfBoundsException(outOfBounds(index, size)); } public E set(int index, E element) { synchronized (l.lock) { rangeCheck(index); checkForComodification(); E x = l.set(index+offset, element); expectedArray = l.getArray(); return x; } } public E get(int index) { synchronized (l.lock) { rangeCheck(index); checkForComodification(); return l.get(index+offset); } } public int size() { synchronized (l.lock) { checkForComodification(); return size; } } public void add(int index, E element) { synchronized (l.lock) { checkForComodification(); if (index < 0 || index > size) throw new IndexOutOfBoundsException (outOfBounds(index, size)); l.add(index+offset, element); expectedArray = l.getArray(); size++; } } public void clear() { synchronized (l.lock) { checkForComodification(); l.removeRange(offset, offset+size); expectedArray = l.getArray(); size = 0; } } public E remove(int index) { synchronized (l.lock) { rangeCheck(index); checkForComodification(); E result = l.remove(index+offset); expectedArray = l.getArray(); size--; return result; } } public boolean remove(Object o) { int index = indexOf(o); if (index == -1) return false; remove(index); return true; } public Iterator iterator() { synchronized (l.lock) { checkForComodification(); return new COWSubListIterator(l, 0, offset, size); } } public ListIterator listIterator(int index) { synchronized (l.lock) { checkForComodification(); if (index < 0 || index > size) throw new IndexOutOfBoundsException (outOfBounds(index, size)); return new COWSubListIterator(l, index, offset, size); } } public List subList(int fromIndex, int toIndex) { synchronized (l.lock) { checkForComodification(); if (fromIndex < 0 || toIndex > size || fromIndex > toIndex) throw new IndexOutOfBoundsException(); return new COWSubList(l, fromIndex + offset, toIndex + offset); } } public void forEach(Consumer action) { if (action == null) throw new NullPointerException(); int lo = offset; int hi = offset + size; Object[] a = expectedArray; if (l.getArray() != a) throw new ConcurrentModificationException(); if (lo < 0 || hi > a.length) throw new IndexOutOfBoundsException(); for (int i = lo; i < hi; ++i) { @SuppressWarnings("unchecked") E e = (E) a[i]; action.accept(e); } } public void replaceAll(UnaryOperator operator) { if (operator == null) throw new NullPointerException(); synchronized (l.lock) { int lo = offset; int hi = offset + size; Object[] elements = expectedArray; if (l.getArray() != elements) throw new ConcurrentModificationException(); int len = elements.length; if (lo < 0 || hi > len) throw new IndexOutOfBoundsException(); Object[] newElements = Arrays.copyOf(elements, len); for (int i = lo; i < hi; ++i) { @SuppressWarnings("unchecked") E e = (E) elements[i]; newElements[i] = operator.apply(e); } l.setArray(expectedArray = newElements); } } public void sort(Comparator c) { synchronized (l.lock) { int lo = offset; int hi = offset + size; Object[] elements = expectedArray; if (l.getArray() != elements) throw new ConcurrentModificationException(); int len = elements.length; if (lo < 0 || hi > len) throw new IndexOutOfBoundsException(); Object[] newElements = Arrays.copyOf(elements, len); @SuppressWarnings("unchecked") E[] es = (E[])newElements; Arrays.sort(es, lo, hi, c); l.setArray(expectedArray = newElements); } } public boolean removeAll(Collection c) { if (c == null) throw new NullPointerException(); boolean removed = false; synchronized (l.lock) { int n = size; if (n > 0) { int lo = offset; int hi = offset + n; Object[] elements = expectedArray; if (l.getArray() != elements) throw new ConcurrentModificationException(); int len = elements.length; if (lo < 0 || hi > len) throw new IndexOutOfBoundsException(); int newSize = 0; Object[] temp = new Object[n]; for (int i = lo; i < hi; ++i) { Object element = elements[i]; if (!c.contains(element)) temp[newSize++] = element; } if (newSize != n) { Object[] newElements = new Object[len - n + newSize]; System.arraycopy(elements, 0, newElements, 0, lo); System.arraycopy(temp, 0, newElements, lo, newSize); System.arraycopy(elements, hi, newElements, lo + newSize, len - hi); size = newSize; removed = true; l.setArray(expectedArray = newElements); } } } return removed; } public boolean retainAll(Collection c) { if (c == null) throw new NullPointerException(); boolean removed = false; synchronized (l.lock) { int n = size; if (n > 0) { int lo = offset; int hi = offset + n; Object[] elements = expectedArray; if (l.getArray() != elements) throw new ConcurrentModificationException(); int len = elements.length; if (lo < 0 || hi > len) throw new IndexOutOfBoundsException(); int newSize = 0; Object[] temp = new Object[n]; for (int i = lo; i < hi; ++i) { Object element = elements[i]; if (c.contains(element)) temp[newSize++] = element; } if (newSize != n) { Object[] newElements = new Object[len - n + newSize]; System.arraycopy(elements, 0, newElements, 0, lo); System.arraycopy(temp, 0, newElements, lo, newSize); System.arraycopy(elements, hi, newElements, lo + newSize, len - hi); size = newSize; removed = true; l.setArray(expectedArray = newElements); } } } return removed; } public boolean removeIf(Predicate filter) { if (filter == null) throw new NullPointerException(); boolean removed = false; synchronized (l.lock) { int n = size; if (n > 0) { int lo = offset; int hi = offset + n; Object[] elements = expectedArray; if (l.getArray() != elements) throw new ConcurrentModificationException(); int len = elements.length; if (lo < 0 || hi > len) throw new IndexOutOfBoundsException(); int newSize = 0; Object[] temp = new Object[n]; for (int i = lo; i < hi; ++i) { @SuppressWarnings("unchecked") E e = (E) elements[i]; if (!filter.test(e)) temp[newSize++] = e; } if (newSize != n) { Object[] newElements = new Object[len - n + newSize]; System.arraycopy(elements, 0, newElements, 0, lo); System.arraycopy(temp, 0, newElements, lo, newSize); System.arraycopy(elements, hi, newElements, lo + newSize, len - hi); size = newSize; removed = true; l.setArray(expectedArray = newElements); } } } return removed; } public Spliterator spliterator() { int lo = offset; int hi = offset + size; Object[] a = expectedArray; if (l.getArray() != a) throw new ConcurrentModificationException(); if (lo < 0 || hi > a.length) throw new IndexOutOfBoundsException(); return Spliterators.spliterator (a, lo, hi, Spliterator.IMMUTABLE | Spliterator.ORDERED); } } private static class COWSubListIterator implements ListIterator { private final ListIterator it; private final int offset; private final int size; COWSubListIterator(List 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 action) { Objects.requireNonNull(action); while (nextIndex() < size) { action.accept(it.next()); } } } // Support for resetting lock while deserializing private void resetLock() { U.putObjectVolatile(this, LOCK, new Object()); } private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe(); private static final long LOCK; static { try { LOCK = U.objectFieldOffset (CopyOnWriteArrayList.class.getDeclaredField("lock")); } catch (ReflectiveOperationException e) { throw new Error(e); } } }