Java tutorial
/* * Copyright (C) 2007 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.collect; import com.google.common.annotations.GwtCompatible; import com.google.common.base.Objects; import java.util.Collection; import java.util.Iterator; import javax.annotation.Nullable; /** * A collection which forwards all its method calls to another collection. * Subclasses should override one or more methods to modify the behavior of the * backing collection as desired per the <a * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. * * <p><b>Warning:</b> The methods of {@code ForwardingCollection} forward * <b>indiscriminately</b> to the methods of the delegate. For example, * overriding {@link #add} alone <b>will not</b> change the behavior of {@link * #addAll}, which can lead to unexpected behavior. In this case, you should * override {@code addAll} as well, either providing your own implementation, or * delegating to the provided {@code standardAddAll} method. * * <p>The {@code standard} methods are not guaranteed to be thread-safe, even * when all of the methods that they depend on are thread-safe. * * @author Kevin Bourrillion * @author Louis Wasserman * @since 2.0 */ @GwtCompatible public abstract class ForwardingCollection<E> extends ForwardingObject implements Collection<E> { // TODO(lowasser): identify places where thread safety is actually lost /** Constructor for use by subclasses. */ protected ForwardingCollection() { } @Override protected abstract Collection<E> delegate(); @Override public Iterator<E> iterator() { return delegate().iterator(); } @Override public int size() { return delegate().size(); } @Override public boolean removeAll(Collection<?> collection) { return delegate().removeAll(collection); } @Override public boolean isEmpty() { return delegate().isEmpty(); } @Override public boolean contains(Object object) { return delegate().contains(object); } @Override public boolean add(E element) { return delegate().add(element); } @Override public boolean remove(Object object) { return delegate().remove(object); } @Override public boolean containsAll(Collection<?> collection) { return delegate().containsAll(collection); } @Override public boolean addAll(Collection<? extends E> collection) { return delegate().addAll(collection); } @Override public boolean retainAll(Collection<?> collection) { return delegate().retainAll(collection); } @Override public void clear() { delegate().clear(); } @Override public Object[] toArray() { return delegate().toArray(); } @Override public <T> T[] toArray(T[] array) { return delegate().toArray(array); } /** * A sensible definition of {@link #contains} in terms of {@link #iterator}. * If you override {@link #iterator}, you may wish to override {@link * #contains} to forward to this implementation. * * @since 7.0 */ protected boolean standardContains(@Nullable Object object) { return Iterators.contains(iterator(), object); } /** * A sensible definition of {@link #containsAll} in terms of {@link #contains} * . If you override {@link #contains}, you may wish to override {@link * #containsAll} to forward to this implementation. * * @since 7.0 */ protected boolean standardContainsAll(Collection<?> collection) { return Collections2.containsAllImpl(this, collection); } /** * A sensible definition of {@link #addAll} in terms of {@link #add}. If you * override {@link #add}, you may wish to override {@link #addAll} to forward * to this implementation. * * @since 7.0 */ protected boolean standardAddAll(Collection<? extends E> collection) { return Iterators.addAll(this, collection.iterator()); } /** * A sensible definition of {@link #remove} in terms of {@link #iterator}, * using the iterator's {@code remove} method. If you override {@link * #iterator}, you may wish to override {@link #remove} to forward to this * implementation. * * @since 7.0 */ protected boolean standardRemove(@Nullable Object object) { Iterator<E> iterator = iterator(); while (iterator.hasNext()) { if (Objects.equal(iterator.next(), object)) { iterator.remove(); return true; } } return false; } /** * A sensible definition of {@link #removeAll} in terms of {@link #iterator}, * using the iterator's {@code remove} method. If you override {@link * #iterator}, you may wish to override {@link #removeAll} to forward to this * implementation. * * @since 7.0 */ protected boolean standardRemoveAll(Collection<?> collection) { return Iterators.removeAll(iterator(), collection); } /** * A sensible definition of {@link #retainAll} in terms of {@link #iterator}, * using the iterator's {@code remove} method. If you override {@link * #iterator}, you may wish to override {@link #retainAll} to forward to this * implementation. * * @since 7.0 */ protected boolean standardRetainAll(Collection<?> collection) { return Iterators.retainAll(iterator(), collection); } /** * A sensible definition of {@link #clear} in terms of {@link #iterator}, * using the iterator's {@code remove} method. If you override {@link * #iterator}, you may wish to override {@link #clear} to forward to this * implementation. * * @since 7.0 */ protected void standardClear() { Iterators.clear(iterator()); } /** * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}. * If you override {@link #isEmpty}, you may wish to override {@link #isEmpty} * to forward to this implementation. Alternately, it may be more efficient to * implement {@code isEmpty} as {@code size() == 0}. * * @since 7.0 */ protected boolean standardIsEmpty() { return !iterator().hasNext(); } /** * A sensible definition of {@link #toString} in terms of {@link #iterator}. * If you override {@link #iterator}, you may wish to override {@link * #toString} to forward to this implementation. * * @since 7.0 */ protected String standardToString() { return Collections2.toStringImpl(this); } /** * A sensible definition of {@link #toArray()} in terms of {@link * #toArray(Object[])}. If you override {@link #toArray(Object[])}, you may * wish to override {@link #toArray} to forward to this implementation. * * @since 7.0 */ protected Object[] standardToArray() { Object[] newArray = new Object[size()]; return toArray(newArray); } /** * A sensible definition of {@link #toArray(Object[])} in terms of {@link * #size} and {@link #iterator}. If you override either of these methods, you * may wish to override {@link #toArray} to forward to this implementation. * * @since 7.0 */ protected <T> T[] standardToArray(T[] array) { return ObjectArrays.toArrayImpl(this, array); } }