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.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.base.Objects; import java.util.Collection; import java.util.Iterator; import java.util.Set; import javax.annotation.Nullable; /** * A multiset which forwards all its method calls to another multiset. * Subclasses should override one or more methods to modify the behavior of the * backing multiset as desired per the <a * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. * * <p><b>Warning:</b> The methods of {@code ForwardingMultiset} forward * <b>indiscriminately</b> to the methods of the delegate. For example, * overriding {@link #add(Object, int)} alone <b>will not</b> change the * behavior of {@link #add(Object)}, which can lead to unexpected behavior. In * this case, you should override {@code add(Object)} as well, either providing * your own implementation, or delegating to the provided {@code standardAdd} * method. * * <p>The {@code standard} methods and any collection views they return 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 ForwardingMultiset<E> extends ForwardingCollection<E> implements Multiset<E> { /** Constructor for use by subclasses. */ protected ForwardingMultiset() { } @Override protected abstract Multiset<E> delegate(); @Override public int count(Object element) { return delegate().count(element); } @Override public int add(E element, int occurrences) { return delegate().add(element, occurrences); } @Override public int remove(Object element, int occurrences) { return delegate().remove(element, occurrences); } @Override public Set<E> elementSet() { return delegate().elementSet(); } @Override public Set<Entry<E>> entrySet() { return delegate().entrySet(); } @Override public boolean equals(@Nullable Object object) { return object == this || delegate().equals(object); } @Override public int hashCode() { return delegate().hashCode(); } @Override public int setCount(E element, int count) { return delegate().setCount(element, count); } @Override public boolean setCount(E element, int oldCount, int newCount) { return delegate().setCount(element, oldCount, newCount); } /** * A sensible definition of {@link #contains} in terms of {@link #count}. If * you override {@link #count}, you may wish to override {@link #contains} to * forward to this implementation. * * @since 7.0 */ @Override protected boolean standardContains(@Nullable Object object) { return count(object) > 0; } /** * A sensible definition of {@link #clear} in terms of the {@code iterator} * method of {@link #entrySet}. If you override {@link #entrySet}, you may * wish to override {@link #clear} to forward to this implementation. * * @since 7.0 */ @Override protected void standardClear() { Iterators.clear(entrySet().iterator()); } /** * A sensible, albeit inefficient, definition of {@link #count} in terms of * {@link #entrySet}. If you override {@link #entrySet}, you may wish to * override {@link #count} to forward to this implementation. * * @since 7.0 */ @Beta protected int standardCount(@Nullable Object object) { for (Entry<?> entry : this.entrySet()) { if (Objects.equal(entry.getElement(), object)) { return entry.getCount(); } } return 0; } /** * A sensible definition of {@link #add(Object)} in terms of {@link * #add(Object, int)}. If you override {@link #add(Object, int)}, you may * wish to override {@link #add(Object)} to forward to this implementation. * * @since 7.0 */ protected boolean standardAdd(E element) { add(element, 1); return true; } /** * A sensible definition of {@link #addAll(Collection)} in terms of {@link * #add(Object)} and {@link #add(Object, int)}. If you override either of * these methods, you may wish to override {@link #addAll(Collection)} to * forward to this implementation. * * @since 7.0 */ @Beta @Override protected boolean standardAddAll(Collection<? extends E> elementsToAdd) { return Multisets.addAllImpl(this, elementsToAdd); } /** * A sensible definition of {@link #remove(Object)} in terms of {@link * #remove(Object, int)}. If you override {@link #remove(Object, int)}, you * may wish to override {@link #remove(Object)} to forward to this * implementation. * * @since 7.0 */ @Override protected boolean standardRemove(Object element) { return remove(element, 1) > 0; } /** * A sensible definition of {@link #removeAll} in terms of the {@code * removeAll} method of {@link #elementSet}. If you override {@link * #elementSet}, you may wish to override {@link #removeAll} to forward to * this implementation. * * @since 7.0 */ @Override protected boolean standardRemoveAll(Collection<?> elementsToRemove) { return Multisets.removeAllImpl(this, elementsToRemove); } /** * A sensible definition of {@link #retainAll} in terms of the {@code * retainAll} method of {@link #elementSet}. If you override {@link * #elementSet}, you may wish to override {@link #retainAll} to forward to * this implementation. * * @since 7.0 */ @Override protected boolean standardRetainAll(Collection<?> elementsToRetain) { return Multisets.retainAllImpl(this, elementsToRetain); } /** * A sensible definition of {@link #setCount(Object, int)} in terms of {@link * #count(Object)}, {@link #add(Object, int)}, and {@link #remove(Object, * int)}. {@link #entrySet()}. If you override any of these methods, you may * wish to override {@link #setCount(Object, int)} to forward to this * implementation. * * @since 7.0 */ protected int standardSetCount(E element, int count) { return Multisets.setCountImpl(this, element, count); } /** * A sensible definition of {@link #setCount(Object, int, int)} in terms of * {@link #count(Object)} and {@link #setCount(Object, int)}. If you override * either of these methods, you may wish to override {@link #setCount(Object, * int, int)} to forward to this implementation. * * @since 7.0 */ protected boolean standardSetCount(E element, int oldCount, int newCount) { return Multisets.setCountImpl(this, element, oldCount, newCount); } /** * A sensible implementation of {@link Multiset#elementSet} in terms of the * following methods: {@link ForwardingMultiset#clear}, {@link * ForwardingMultiset#contains}, {@link ForwardingMultiset#containsAll}, * {@link ForwardingMultiset#count}, {@link ForwardingMultiset#isEmpty}, the * {@link Set#size} and {@link Set#iterator} methods of {@link * ForwardingMultiset#entrySet}, and {@link ForwardingMultiset#remove(Object, * int)}. In many situations, you may wish to override {@link * ForwardingMultiset#elementSet} to forward to this implementation or a * subclass thereof. * * @since 10.0 */ @Beta protected class StandardElementSet extends Multisets.ElementSet<E> { /** Constructor for use by subclasses. */ public StandardElementSet() { } @Override Multiset<E> multiset() { return ForwardingMultiset.this; } } /** * A sensible definition of {@link #iterator} in terms of {@link #entrySet} * and {@link #remove(Object)}. If you override either of these methods, you * may wish to override {@link #iterator} to forward to this implementation. * * @since 7.0 */ protected Iterator<E> standardIterator() { return Multisets.iteratorImpl(this); } /** * A sensible, albeit inefficient, definition of {@link #size} in terms of * {@link #entrySet}. If you override {@link #entrySet}, you may wish to * override {@link #size} to forward to this implementation. * * @since 7.0 */ protected int standardSize() { return Multisets.sizeImpl(this); } /** * A sensible, albeit inefficient, definition of {@link #size} in terms of * {@code entrySet().size()} and {@link #count}. If you override either of * these methods, you may wish to override {@link #size} to forward to this * implementation. * * @since 7.0 */ protected boolean standardEquals(@Nullable Object object) { return Multisets.equalsImpl(this, object); } /** * A sensible definition of {@link #hashCode} as {@code entrySet().hashCode()} * . If you override {@link #entrySet}, you may wish to override {@link * #hashCode} to forward to this implementation. * * @since 7.0 */ protected int standardHashCode() { return entrySet().hashCode(); } /** * A sensible definition of {@link #toString} as {@code entrySet().toString()} * . If you override {@link #entrySet}, you may wish to override {@link * #toString} to forward to this implementation. * * @since 7.0 */ @Override protected String standardToString() { return entrySet().toString(); } }