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 com.google.errorprone.annotations.CanIgnoreReturnValue; 023import java.util.Collection; 024import java.util.Iterator; 025import java.util.Map; 026import java.util.Set; 027import javax.annotation.CheckForNull; 028import org.checkerframework.checker.nullness.qual.Nullable; 029 030/** 031 * A map which forwards all its method calls to another map. Subclasses should override one or more 032 * methods to modify the behavior of the backing map as desired per the <a 033 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 034 * 035 * <p><b>Warning:</b> The methods of {@code ForwardingMap} forward <i>indiscriminately</i> to the 036 * methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change the 037 * behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should 038 * override {@code putAll} as well, either providing your own implementation, or delegating to the 039 * provided {@code standardPutAll} method. 040 * 041 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code 042 * default} methods. Instead, it inherits their default implementations. When those implementations 043 * invoke methods, they invoke methods on the {@code ForwardingMap}. 044 * 045 * <p>Each of the {@code standard} methods, where appropriate, use {@link Objects#equal} to test 046 * equality for both keys and values. This may not be the desired behavior for map implementations 047 * that use non-standard notions of key equality, such as a {@code SortedMap} whose comparator is 048 * not consistent with {@code equals}. 049 * 050 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be 051 * thread-safe, even when all of the methods that they depend on are thread-safe. 052 * 053 * @author Kevin Bourrillion 054 * @author Jared Levy 055 * @author Louis Wasserman 056 * @since 2.0 057 */ 058@GwtCompatible 059@ElementTypesAreNonnullByDefault 060public abstract class ForwardingMap<K extends @Nullable Object, V extends @Nullable Object> 061 extends ForwardingObject implements Map<K, V> { 062 // TODO(lowasser): identify places where thread safety is actually lost 063 064 /** Constructor for use by subclasses. */ 065 protected ForwardingMap() {} 066 067 @Override 068 protected abstract Map<K, V> delegate(); 069 070 @Override 071 public int size() { 072 return delegate().size(); 073 } 074 075 @Override 076 public boolean isEmpty() { 077 return delegate().isEmpty(); 078 } 079 080 @CanIgnoreReturnValue 081 @Override 082 @CheckForNull 083 public V remove(@CheckForNull Object key) { 084 return delegate().remove(key); 085 } 086 087 @Override 088 public void clear() { 089 delegate().clear(); 090 } 091 092 @Override 093 public boolean containsKey(@CheckForNull Object key) { 094 return delegate().containsKey(key); 095 } 096 097 @Override 098 public boolean containsValue(@CheckForNull Object value) { 099 return delegate().containsValue(value); 100 } 101 102 @Override 103 @CheckForNull 104 public V get(@CheckForNull Object key) { 105 return delegate().get(key); 106 } 107 108 @CanIgnoreReturnValue 109 @Override 110 @CheckForNull 111 public V put(@ParametricNullness K key, @ParametricNullness V value) { 112 return delegate().put(key, value); 113 } 114 115 @Override 116 public void putAll(Map<? extends K, ? extends V> map) { 117 delegate().putAll(map); 118 } 119 120 @Override 121 public Set<K> keySet() { 122 return delegate().keySet(); 123 } 124 125 @Override 126 public Collection<V> values() { 127 return delegate().values(); 128 } 129 130 @Override 131 public Set<Entry<K, V>> entrySet() { 132 return delegate().entrySet(); 133 } 134 135 @Override 136 public boolean equals(@CheckForNull Object object) { 137 return object == this || delegate().equals(object); 138 } 139 140 @Override 141 public int hashCode() { 142 return delegate().hashCode(); 143 } 144 145 /** 146 * A sensible definition of {@link #putAll(Map)} in terms of {@link #put(Object, Object)}. If you 147 * override {@link #put(Object, Object)}, you may wish to override {@link #putAll(Map)} to forward 148 * to this implementation. 149 * 150 * @since 7.0 151 */ 152 protected void standardPutAll(Map<? extends K, ? extends V> map) { 153 Maps.putAllImpl(this, map); 154 } 155 156 /** 157 * A sensible, albeit inefficient, definition of {@link #remove} in terms of the {@code iterator} 158 * method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link 159 * #remove} to forward to this implementation. 160 * 161 * <p>Alternately, you may wish to override {@link #remove} with {@code keySet().remove}, assuming 162 * that approach would not lead to an infinite loop. 163 * 164 * @since 7.0 165 */ 166 @Beta 167 @CheckForNull 168 protected V standardRemove(@CheckForNull Object key) { 169 Iterator<Entry<K, V>> entryIterator = entrySet().iterator(); 170 while (entryIterator.hasNext()) { 171 Entry<K, V> entry = entryIterator.next(); 172 if (Objects.equal(entry.getKey(), key)) { 173 V value = entry.getValue(); 174 entryIterator.remove(); 175 return value; 176 } 177 } 178 return null; 179 } 180 181 /** 182 * A sensible definition of {@link #clear} in terms of the {@code iterator} method of {@link 183 * #entrySet}. In many cases, you may wish to override {@link #clear} to forward to this 184 * implementation. 185 * 186 * @since 7.0 187 */ 188 protected void standardClear() { 189 Iterators.clear(entrySet().iterator()); 190 } 191 192 /** 193 * A sensible implementation of {@link Map#keySet} in terms of the following methods: {@link 194 * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#isEmpty}, {@link 195 * ForwardingMap#remove}, {@link ForwardingMap#size}, and the {@link Set#iterator} method of 196 * {@link ForwardingMap#entrySet}. In many cases, you may wish to override {@link 197 * ForwardingMap#keySet} to forward to this implementation or a subclass thereof. 198 * 199 * @since 10.0 200 */ 201 @Beta 202 protected class StandardKeySet extends Maps.KeySet<K, V> { 203 /** Constructor for use by subclasses. */ 204 public StandardKeySet() { 205 super(ForwardingMap.this); 206 } 207 } 208 209 /** 210 * A sensible, albeit inefficient, definition of {@link #containsKey} in terms of the {@code 211 * iterator} method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to 212 * override {@link #containsKey} to forward to this implementation. 213 * 214 * @since 7.0 215 */ 216 @Beta 217 protected boolean standardContainsKey(@CheckForNull Object key) { 218 return Maps.containsKeyImpl(this, key); 219 } 220 221 /** 222 * A sensible implementation of {@link Map#values} in terms of the following methods: {@link 223 * ForwardingMap#clear}, {@link ForwardingMap#containsValue}, {@link ForwardingMap#isEmpty}, 224 * {@link ForwardingMap#size}, and the {@link Set#iterator} method of {@link 225 * ForwardingMap#entrySet}. In many cases, you may wish to override {@link ForwardingMap#values} 226 * to forward to this implementation or a subclass thereof. 227 * 228 * @since 10.0 229 */ 230 @Beta 231 protected class StandardValues extends Maps.Values<K, V> { 232 /** Constructor for use by subclasses. */ 233 public StandardValues() { 234 super(ForwardingMap.this); 235 } 236 } 237 238 /** 239 * A sensible definition of {@link #containsValue} in terms of the {@code iterator} method of 240 * {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link 241 * #containsValue} to forward to this implementation. 242 * 243 * @since 7.0 244 */ 245 protected boolean standardContainsValue(@CheckForNull Object value) { 246 return Maps.containsValueImpl(this, value); 247 } 248 249 /** 250 * A sensible implementation of {@link Map#entrySet} in terms of the following methods: {@link 251 * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#get}, {@link 252 * ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, and {@link ForwardingMap#size}. In many 253 * cases, you may wish to override {@link #entrySet} to forward to this implementation or a 254 * subclass thereof. 255 * 256 * @since 10.0 257 */ 258 @Beta 259 protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> { 260 /** Constructor for use by subclasses. */ 261 public StandardEntrySet() {} 262 263 @Override 264 Map<K, V> map() { 265 return ForwardingMap.this; 266 } 267 } 268 269 /** 270 * A sensible definition of {@link #isEmpty} in terms of the {@code iterator} method of {@link 271 * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #isEmpty} to 272 * forward to this implementation. 273 * 274 * @since 7.0 275 */ 276 protected boolean standardIsEmpty() { 277 return !entrySet().iterator().hasNext(); 278 } 279 280 /** 281 * A sensible definition of {@link #equals} in terms of the {@code equals} method of {@link 282 * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #equals} to 283 * forward to this implementation. 284 * 285 * @since 7.0 286 */ 287 protected boolean standardEquals(@CheckForNull Object object) { 288 return Maps.equalsImpl(this, object); 289 } 290 291 /** 292 * A sensible definition of {@link #hashCode} in terms of the {@code iterator} method of {@link 293 * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #hashCode} to 294 * forward to this implementation. 295 * 296 * @since 7.0 297 */ 298 protected int standardHashCode() { 299 return Sets.hashCodeImpl(entrySet()); 300 } 301 302 /** 303 * A sensible definition of {@link #toString} in terms of the {@code iterator} method of {@link 304 * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #toString} to 305 * forward to this implementation. 306 * 307 * @since 7.0 308 */ 309 protected String standardToString() { 310 return Maps.toStringImpl(this); 311 } 312}