1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.collect; 18 19 import com.google.common.annotations.Beta; 20 import com.google.common.annotations.GwtCompatible; 21 import com.google.common.base.Objects; 22 23 import java.util.Map; 24 import java.util.Map.Entry; 25 26 import javax.annotation.Nullable; 27 28 /** 29 * A map entry which forwards all its method calls to another map entry. 30 * Subclasses should override one or more methods to modify the behavior of the 31 * backing map entry as desired per the <a 32 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 33 * 34 * <p><i>Warning:</i> The methods of {@code ForwardingMapEntry} forward 35 * <i>indiscriminately</i> to the methods of the delegate. For example, 36 * overriding {@link #getValue} alone <i>will not</i> change the behavior of 37 * {@link #equals}, which can lead to unexpected behavior. In this case, you 38 * should override {@code equals} as well, either providing your own 39 * implementation, or delegating to the provided {@code standardEquals} method. 40 * 41 * <p>Each of the {@code standard} methods, where appropriate, use {@link 42 * Objects#equal} to test equality for both keys and values. This may not be 43 * the desired behavior for map implementations that use non-standard notions of 44 * key equality, such as the entry of a {@code SortedMap} whose comparator is 45 * not consistent with {@code equals}. 46 * 47 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even 48 * when all of the methods that they depend on are thread-safe. 49 * 50 * @author Mike Bostock 51 * @author Louis Wasserman 52 * @since 2.0 (imported from Google Collections Library) 53 */ 54 @GwtCompatible 55 public abstract class ForwardingMapEntry<K, V> 56 extends ForwardingObject implements Map.Entry<K, V> { 57 // TODO(user): identify places where thread safety is actually lost 58 59 /** Constructor for use by subclasses. */ ForwardingMapEntry()60 protected ForwardingMapEntry() {} 61 delegate()62 @Override protected abstract Map.Entry<K, V> delegate(); 63 64 @Override getKey()65 public K getKey() { 66 return delegate().getKey(); 67 } 68 69 @Override getValue()70 public V getValue() { 71 return delegate().getValue(); 72 } 73 74 @Override setValue(V value)75 public V setValue(V value) { 76 return delegate().setValue(value); 77 } 78 equals(@ullable Object object)79 @Override public boolean equals(@Nullable Object object) { 80 return delegate().equals(object); 81 } 82 hashCode()83 @Override public int hashCode() { 84 return delegate().hashCode(); 85 } 86 87 /** 88 * A sensible definition of {@link #equals(Object)} in terms of {@link 89 * #getKey()} and {@link #getValue()}. If you override either of these 90 * methods, you may wish to override {@link #equals(Object)} to forward to 91 * this implementation. 92 * 93 * @since 7.0 94 */ standardEquals(@ullable Object object)95 protected boolean standardEquals(@Nullable Object object) { 96 if (object instanceof Entry) { 97 Entry<?, ?> that = (Entry<?, ?>) object; 98 return Objects.equal(this.getKey(), that.getKey()) 99 && 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 */ standardHashCode()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 */ standardToString()125 @Beta protected String standardToString() { 126 return getKey() + "=" + getValue(); 127 } 128 } 129