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.Map; import java.util.Set; import javax.annotation.Nullable; /** * A map which forwards all its method calls to another map. Subclasses should * override one or more methods to modify the behavior of the backing map as * desired per the <a * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. * * <p><i>Warning:</i> The methods of {@code ForwardingMap} forward * <i>indiscriminately</i> to the methods of the delegate. For example, * overriding {@link #put} alone <i>will not</i> change the behavior of {@link * #putAll}, which can lead to unexpected behavior. In this case, you should * override {@code putAll} as well, either providing your own implementation, or * delegating to the provided {@code standardPutAll} method. * * <p>Each of the {@code standard} methods, where appropriate, use {@link * Objects#equal} to test equality for both keys and values. This may not be * the desired behavior for map implementations that use non-standard notions of * key equality, such as a {@code SortedMap} whose comparator is not consistent * with {@code equals}. * * <p>The {@code standard} methods and the 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 Jared Levy * @author Louis Wasserman * @since 2.0 */ @GwtCompatible public abstract class ForwardingMap<K, V> extends ForwardingObject implements Map<K, V> { // TODO(lowasser): identify places where thread safety is actually lost /** Constructor for use by subclasses. */ protected ForwardingMap() { } @Override protected abstract Map<K, V> delegate(); @Override public int size() { return delegate().size(); } @Override public boolean isEmpty() { return delegate().isEmpty(); } @Override public V remove(Object object) { return delegate().remove(object); } @Override public void clear() { delegate().clear(); } @Override public boolean containsKey(@Nullable Object key) { return delegate().containsKey(key); } @Override public boolean containsValue(@Nullable Object value) { return delegate().containsValue(value); } @Override public V get(@Nullable Object key) { return delegate().get(key); } @Override public V put(K key, V value) { return delegate().put(key, value); } @Override public void putAll(Map<? extends K, ? extends V> map) { delegate().putAll(map); } @Override public Set<K> keySet() { return delegate().keySet(); } @Override public Collection<V> values() { return delegate().values(); } @Override public Set<Entry<K, V>> entrySet() { return delegate().entrySet(); } @Override public boolean equals(@Nullable Object object) { return object == this || delegate().equals(object); } @Override public int hashCode() { return delegate().hashCode(); } /** * A sensible definition of {@link #putAll(Map)} in terms of {@link * #put(Object, Object)}. If you override {@link #put(Object, Object)}, you * may wish to override {@link #putAll(Map)} to forward to this * implementation. * * @since 7.0 */ protected void standardPutAll(Map<? extends K, ? extends V> map) { Maps.putAllImpl(this, map); } /** * A sensible, albeit inefficient, definition of {@link #remove} in terms of * the {@code iterator} method of {@link #entrySet}. If you override {@link * #entrySet}, you may wish to override {@link #remove} to forward to this * implementation. * * <p>Alternately, you may wish to override {@link #remove} with {@code * keySet().remove}, assuming that approach would not lead to an infinite * loop. * * @since 7.0 */ @Beta protected V standardRemove(@Nullable Object key) { Iterator<Entry<K, V>> entryIterator = entrySet().iterator(); while (entryIterator.hasNext()) { Entry<K, V> entry = entryIterator.next(); if (Objects.equal(entry.getKey(), key)) { V value = entry.getValue(); entryIterator.remove(); return value; } } return null; } /** * A sensible definition of {@link #clear} in terms of the {@code iterator} * method of {@link #entrySet}. In many cases, you may wish to override * {@link #clear} to forward to this implementation. * * @since 7.0 */ protected void standardClear() { Iterators.clear(entrySet().iterator()); } /** * A sensible implementation of {@link Map#keySet} in terms of the following * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey}, * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, {@link * ForwardingMap#size}, and the {@link Set#iterator} method of {@link * ForwardingMap#entrySet}. In many cases, you may wish to override {@link * ForwardingMap#keySet} to forward to this implementation or a subclass * thereof. * * @since 10.0 */ @Beta protected class StandardKeySet extends Maps.KeySet<K, V> { /** Constructor for use by subclasses. */ public StandardKeySet() { super(ForwardingMap.this); } } /** * A sensible, albeit inefficient, definition of {@link #containsKey} in terms * of the {@code iterator} method of {@link #entrySet}. If you override {@link * #entrySet}, you may wish to override {@link #containsKey} to forward to * this implementation. * * @since 7.0 */ @Beta protected boolean standardContainsKey(@Nullable Object key) { return Maps.containsKeyImpl(this, key); } /** * A sensible implementation of {@link Map#values} in terms of the following * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsValue}, * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#size}, and the {@link * Set#iterator} method of {@link ForwardingMap#entrySet}. In many cases, you * may wish to override {@link ForwardingMap#values} to forward to this * implementation or a subclass thereof. * * @since 10.0 */ @Beta protected class StandardValues extends Maps.Values<K, V> { /** Constructor for use by subclasses. */ public StandardValues() { super(ForwardingMap.this); } } /** * A sensible definition of {@link #containsValue} in terms of the {@code * iterator} method of {@link #entrySet}. If you override {@link #entrySet}, * you may wish to override {@link #containsValue} to forward to this * implementation. * * @since 7.0 */ protected boolean standardContainsValue(@Nullable Object value) { return Maps.containsValueImpl(this, value); } /** * A sensible implementation of {@link Map#entrySet} in terms of the following * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey}, * {@link ForwardingMap#get}, {@link ForwardingMap#isEmpty}, {@link * ForwardingMap#remove}, and {@link ForwardingMap#size}. In many cases, you * may wish to override {@link #entrySet} to forward to this implementation * or a subclass thereof. * * @since 10.0 */ @Beta protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> { /** Constructor for use by subclasses. */ public StandardEntrySet() { } @Override Map<K, V> map() { return ForwardingMap.this; } } /** * A sensible definition of {@link #isEmpty} in terms of the {@code iterator} * method of {@link #entrySet}. If you override {@link #entrySet}, you may * wish to override {@link #isEmpty} to forward to this implementation. * * @since 7.0 */ protected boolean standardIsEmpty() { return !entrySet().iterator().hasNext(); } /** * A sensible definition of {@link #equals} in terms of the {@code equals} * method of {@link #entrySet}. If you override {@link #entrySet}, you may * wish to override {@link #equals} to forward to this implementation. * * @since 7.0 */ protected boolean standardEquals(@Nullable Object object) { return Maps.equalsImpl(this, object); } /** * A sensible definition of {@link #hashCode} in terms of the {@code iterator} * method of {@link #entrySet}. If you override {@link #entrySet}, you may * wish to override {@link #hashCode} to forward to this implementation. * * @since 7.0 */ protected int standardHashCode() { return Sets.hashCodeImpl(entrySet()); } /** * A sensible definition of {@link #toString} in terms of the {@code iterator} * method of {@link #entrySet}. If you override {@link #entrySet}, you may * wish to override {@link #toString} to forward to this implementation. * * @since 7.0 */ protected String standardToString() { return Maps.toStringImpl(this); } }