diff options
Diffstat (limited to 'guava/src/com/google/common/collect/ForwardingMapEntry.java')
-rw-r--r-- | guava/src/com/google/common/collect/ForwardingMapEntry.java | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/guava/src/com/google/common/collect/ForwardingMapEntry.java b/guava/src/com/google/common/collect/ForwardingMapEntry.java new file mode 100644 index 0000000..ff201a5 --- /dev/null +++ b/guava/src/com/google/common/collect/ForwardingMapEntry.java @@ -0,0 +1,128 @@ +/* + * Copyright (C) 2007 The Guava Authors + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package com.google.common.collect; + +import com.google.common.annotations.Beta; +import com.google.common.annotations.GwtCompatible; +import com.google.common.base.Objects; + +import java.util.Map; +import java.util.Map.Entry; + +import javax.annotation.Nullable; + +/** + * A map entry which forwards all its method calls to another map entry. + * Subclasses should override one or more methods to modify the behavior of the + * backing map entry as desired per the <a + * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. + * + * <p><i>Warning:</i> The methods of {@code ForwardingMapEntry} forward + * <i>indiscriminately</i> to the methods of the delegate. For example, + * overriding {@link #getValue} alone <i>will not</i> change the behavior of + * {@link #equals}, which can lead to unexpected behavior. In this case, you + * should override {@code equals} as well, either providing your own + * implementation, or delegating to the provided {@code standardEquals} method. + * + * <p>Each of the {@code standard} methods, where appropriate, use {@link + * Objects#equal} to test equality for both keys and values. This may not be + * the desired behavior for map implementations that use non-standard notions of + * key equality, such as the entry of a {@code SortedMap} whose comparator is + * not consistent with {@code equals}. + * + * <p>The {@code standard} methods are not guaranteed to be thread-safe, even + * when all of the methods that they depend on are thread-safe. + * + * @author Mike Bostock + * @author Louis Wasserman + * @since 2.0 (imported from Google Collections Library) + */ +@GwtCompatible +public abstract class ForwardingMapEntry<K, V> + extends ForwardingObject implements Map.Entry<K, V> { + // TODO(user): identify places where thread safety is actually lost + + /** Constructor for use by subclasses. */ + protected ForwardingMapEntry() {} + + @Override protected abstract Map.Entry<K, V> delegate(); + + @Override + public K getKey() { + return delegate().getKey(); + } + + @Override + public V getValue() { + return delegate().getValue(); + } + + @Override + public V setValue(V value) { + return delegate().setValue(value); + } + + @Override public boolean equals(@Nullable Object object) { + return delegate().equals(object); + } + + @Override public int hashCode() { + return delegate().hashCode(); + } + + /** + * A sensible definition of {@link #equals(Object)} in terms of {@link + * #getKey()} and {@link #getValue()}. If you override either of these + * methods, you may wish to override {@link #equals(Object)} to forward to + * this implementation. + * + * @since 7.0 + */ + @Beta protected boolean standardEquals(@Nullable Object object) { + if (object instanceof Entry) { + Entry<?, ?> that = (Entry<?, ?>) object; + return Objects.equal(this.getKey(), that.getKey()) + && Objects.equal(this.getValue(), that.getValue()); + } + return false; + } + + /** + * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()} + * and {@link #getValue()}. If you override either of these methods, you may + * wish to override {@link #hashCode()} to forward to this implementation. + * + * @since 7.0 + */ + @Beta protected int standardHashCode() { + K k = getKey(); + V v = getValue(); + return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode()); + } + + /** + * A sensible definition of {@link #toString} in terms of {@link + * #getKey} and {@link #getValue}. If you override either of these + * methods, you may wish to override {@link #equals} to forward to this + * implementation. + * + * @since 7.0 + */ + @Beta protected String standardToString() { + return getKey() + "=" + getValue(); + } +} |