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.CheckForNull; 025import org.checkerframework.checker.nullness.qual.Nullable; 026 027/** 028 * A map entry which forwards all its method calls to another map entry. Subclasses should override 029 * one or more methods to modify the behavior of the 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 <i>indiscriminately</i> to 033 * the methods of the delegate. For example, overriding {@link #getValue} alone <i>will not</i> 034 * change the behavior of {@link #equals}, which can lead to unexpected behavior. In this case, you 035 * should override {@code equals} as well, either providing your own implementation, or delegating 036 * to the provided {@code standardEquals} method. 037 * 038 * <p>Each of the {@code standard} methods, where appropriate, use {@link Objects#equal} to test 039 * equality for both keys and values. This may not be the desired behavior for map implementations 040 * that use non-standard notions of key equality, such as the entry of a {@code SortedMap} whose 041 * comparator is not consistent with {@code equals}. 042 * 043 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the 044 * methods that they depend on are thread-safe. 045 * 046 * @author Mike Bostock 047 * @author Louis Wasserman 048 * @since 2.0 049 */ 050@GwtCompatible 051@ElementTypesAreNonnullByDefault 052public abstract class ForwardingMapEntry<K extends @Nullable Object, V extends @Nullable Object> 053 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 Entry<K, V> delegate(); 061 062 @Override 063 @ParametricNullness 064 public K getKey() { 065 return delegate().getKey(); 066 } 067 068 @Override 069 @ParametricNullness 070 public V getValue() { 071 return delegate().getValue(); 072 } 073 074 @Override 075 @ParametricNullness 076 public V setValue(@ParametricNullness V value) { 077 return delegate().setValue(value); 078 } 079 080 @Override 081 public boolean equals(@CheckForNull Object object) { 082 return delegate().equals(object); 083 } 084 085 @Override 086 public int hashCode() { 087 return delegate().hashCode(); 088 } 089 090 /** 091 * A sensible definition of {@link #equals(Object)} in terms of {@link #getKey()} and {@link 092 * #getValue()}. If you override either of these methods, you may wish to override {@link 093 * #equals(Object)} to forward to this implementation. 094 * 095 * @since 7.0 096 */ 097 protected boolean standardEquals(@CheckForNull Object object) { 098 if (object instanceof Entry) { 099 Entry<?, ?> that = (Entry<?, ?>) object; 100 return Objects.equal(this.getKey(), that.getKey()) 101 && Objects.equal(this.getValue(), that.getValue()); 102 } 103 return false; 104 } 105 106 /** 107 * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} and {@link 108 * #getValue()}. If you override either of these methods, you may wish to override {@link 109 * #hashCode()} to forward to this implementation. 110 * 111 * @since 7.0 112 */ 113 protected int standardHashCode() { 114 K k = getKey(); 115 V v = getValue(); 116 return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode()); 117 } 118 119 /** 120 * A sensible definition of {@link #toString} in terms of {@link #getKey} and {@link #getValue}. 121 * If you override either of these methods, you may wish to override {@link #equals} to forward to 122 * this implementation. 123 * 124 * @since 7.0 125 */ 126 @Beta 127 protected String standardToString() { 128 return getKey() + "=" + getValue(); 129 } 130}