001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtCompatible; 021import com.google.common.base.Objects; 022import java.util.Map; 023import java.util.Map.Entry; 024import javax.annotation.Nullable; 025 026/** 027 * A map entry which forwards all its method calls to another map entry. 028 * Subclasses should override one or more methods to modify the behavior of the 029 * backing map entry as desired per the <a 030 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 031 * 032 * <p><b>Warning:</b> The methods of {@code ForwardingMapEntry} forward 033 * <i>indiscriminately</i> to the methods of the delegate. For example, 034 * overriding {@link #getValue} alone <i>will not</i> change the behavior of 035 * {@link #equals}, which can lead to unexpected behavior. In this case, you 036 * should override {@code equals} as well, either providing your own 037 * implementation, or delegating to the provided {@code standardEquals} method. 038 * 039 * <p>Each of the {@code standard} methods, where appropriate, use {@link 040 * Objects#equal} to test equality for both keys and values. This may not be 041 * the desired behavior for map implementations that use non-standard notions of 042 * key equality, such as the entry of a {@code SortedMap} whose comparator is 043 * not consistent with {@code equals}. 044 * 045 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even 046 * when all of the methods that they depend on are thread-safe. 047 * 048 * @author Mike Bostock 049 * @author Louis Wasserman 050 * @since 2.0 051 */ 052@GwtCompatible 053public abstract class ForwardingMapEntry<K, V> extends ForwardingObject implements Map.Entry<K, V> { 054 // TODO(lowasser): identify places where thread safety is actually lost 055 056 /** Constructor for use by subclasses. */ 057 protected ForwardingMapEntry() {} 058 059 @Override 060 protected abstract Map.Entry<K, V> delegate(); 061 062 @Override 063 public K getKey() { 064 return delegate().getKey(); 065 } 066 067 @Override 068 public V getValue() { 069 return delegate().getValue(); 070 } 071 072 @Override 073 public V setValue(V value) { 074 return delegate().setValue(value); 075 } 076 077 @Override 078 public boolean equals(@Nullable Object object) { 079 return delegate().equals(object); 080 } 081 082 @Override 083 public int hashCode() { 084 return delegate().hashCode(); 085 } 086 087 /** 088 * A sensible definition of {@link #equals(Object)} in terms of {@link 089 * #getKey()} and {@link #getValue()}. If you override either of these 090 * methods, you may wish to override {@link #equals(Object)} to forward to 091 * this implementation. 092 * 093 * @since 7.0 094 */ 095 protected boolean standardEquals(@Nullable Object object) { 096 if (object instanceof Entry) { 097 Entry<?, ?> that = (Entry<?, ?>) object; 098 return Objects.equal(this.getKey(), that.getKey()) 099 && Objects.equal(this.getValue(), that.getValue()); 100 } 101 return false; 102 } 103 104 /** 105 * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} 106 * and {@link #getValue()}. If you override either of these methods, you may 107 * wish to override {@link #hashCode()} to forward to this implementation. 108 * 109 * @since 7.0 110 */ 111 protected int standardHashCode() { 112 K k = getKey(); 113 V v = getValue(); 114 return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode()); 115 } 116 117 /** 118 * A sensible definition of {@link #toString} in terms of {@link 119 * #getKey} and {@link #getValue}. If you override either of these 120 * methods, you may wish to override {@link #equals} to forward to this 121 * implementation. 122 * 123 * @since 7.0 124 */ 125 @Beta 126 protected String standardToString() { 127 return getKey() + "=" + getValue(); 128 } 129}