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.GwtCompatible; 020import com.google.common.base.Objects; 021import java.util.Map; 022import java.util.Map.Entry; 023import javax.annotation.CheckForNull; 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 050@ElementTypesAreNonnullByDefault 051public abstract class ForwardingMapEntry<K extends @Nullable Object, V extends @Nullable Object> 052 extends ForwardingObject implements Map.Entry<K, V> { 053 // TODO(lowasser): identify places where thread safety is actually lost 054 055 /** Constructor for use by subclasses. */ 056 protected ForwardingMapEntry() {} 057 058 @Override 059 protected abstract Entry<K, V> delegate(); 060 061 @Override 062 @ParametricNullness 063 public K getKey() { 064 return delegate().getKey(); 065 } 066 067 @Override 068 @ParametricNullness 069 public V getValue() { 070 return delegate().getValue(); 071 } 072 073 @Override 074 @ParametricNullness 075 public V setValue(@ParametricNullness V value) { 076 return delegate().setValue(value); 077 } 078 079 @Override 080 public boolean equals(@CheckForNull Object object) { 081 return delegate().equals(object); 082 } 083 084 @Override 085 public int hashCode() { 086 return delegate().hashCode(); 087 } 088 089 /** 090 * A sensible definition of {@link #equals(Object)} in terms of {@link #getKey()} and {@link 091 * #getValue()}. If you override either of these methods, you may wish to override {@link 092 * #equals(Object)} to forward to this implementation. 093 * 094 * @since 7.0 095 */ 096 protected boolean standardEquals(@CheckForNull Object object) { 097 if (object instanceof Entry) { 098 Entry<?, ?> that = (Entry<?, ?>) object; 099 return Objects.equal(this.getKey(), that.getKey()) 100 && Objects.equal(this.getValue(), that.getValue()); 101 } 102 return false; 103 } 104 105 /** 106 * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} and {@link 107 * #getValue()}. If you override either of these methods, you may wish to override {@link 108 * #hashCode()} to forward to this implementation. 109 * 110 * @since 7.0 111 */ 112 protected int standardHashCode() { 113 K k = getKey(); 114 V v = getValue(); 115 return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode()); 116 } 117 118 /** 119 * A sensible definition of {@link #toString} in terms of {@link #getKey} and {@link #getValue}. 120 * If you override either of these methods, you may wish to override {@link #equals} to forward to 121 * this implementation. 122 * 123 * @since 7.0 124 */ 125 protected String standardToString() { 126 return getKey() + "=" + getValue(); 127 } 128}