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 org.checkerframework.checker.nullness.qual.Nullable; 025 026/** 027 * A map entry which forwards all its method calls to another map entry. Subclasses should override 028 * one or more methods to modify the behavior of the backing map entry as desired per the <a 029 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 030 * 031 * <p><b>Warning:</b> The methods of {@code ForwardingMapEntry} forward <i>indiscriminately</i> to 032 * the methods of the delegate. For example, overriding {@link #getValue} alone <i>will not</i> 033 * change the behavior of {@link #equals}, which can lead to unexpected behavior. In this case, you 034 * should override {@code equals} as well, either providing your own implementation, or delegating 035 * to the provided {@code standardEquals} method. 036 * 037 * <p>Each of the {@code standard} methods, where appropriate, use {@link Objects#equal} to test 038 * equality for both keys and values. This may not be the desired behavior for map implementations 039 * that use non-standard notions of key equality, such as the entry of a {@code SortedMap} whose 040 * comparator is not consistent with {@code equals}. 041 * 042 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the 043 * methods that they depend on are thread-safe. 044 * 045 * @author Mike Bostock 046 * @author Louis Wasserman 047 * @since 2.0 048 */ 049@GwtCompatible 050public abstract class ForwardingMapEntry<K, V> extends ForwardingObject implements Map.Entry<K, V> { 051 // TODO(lowasser): identify places where thread safety is actually lost 052 053 /** Constructor for use by subclasses. */ 054 protected ForwardingMapEntry() {} 055 056 @Override 057 protected abstract Entry<K, V> delegate(); 058 059 @Override 060 public K getKey() { 061 return delegate().getKey(); 062 } 063 064 @Override 065 public V getValue() { 066 return delegate().getValue(); 067 } 068 069 @Override 070 public V setValue(V value) { 071 return delegate().setValue(value); 072 } 073 074 @Override 075 public boolean equals(@Nullable Object object) { 076 return delegate().equals(object); 077 } 078 079 @Override 080 public int hashCode() { 081 return delegate().hashCode(); 082 } 083 084 /** 085 * A sensible definition of {@link #equals(Object)} in terms of {@link #getKey()} and {@link 086 * #getValue()}. If you override either of these methods, you may wish to override {@link 087 * #equals(Object)} to forward to this implementation. 088 * 089 * @since 7.0 090 */ 091 protected boolean standardEquals(@Nullable Object object) { 092 if (object instanceof Entry) { 093 Entry<?, ?> that = (Entry<?, ?>) object; 094 return Objects.equal(this.getKey(), that.getKey()) 095 && Objects.equal(this.getValue(), that.getValue()); 096 } 097 return false; 098 } 099 100 /** 101 * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} and {@link 102 * #getValue()}. If you override either of these methods, you may wish to override {@link 103 * #hashCode()} to forward to this implementation. 104 * 105 * @since 7.0 106 */ 107 protected int standardHashCode() { 108 K k = getKey(); 109 V v = getValue(); 110 return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode()); 111 } 112 113 /** 114 * A sensible definition of {@link #toString} in terms of {@link #getKey} and {@link #getValue}. 115 * If you override either of these methods, you may wish to override {@link #equals} to forward to 116 * this implementation. 117 * 118 * @since 7.0 119 */ 120 @Beta 121 protected String standardToString() { 122 return getKey() + "=" + getValue(); 123 } 124}