com.google.common.collect.ForwardingMapEntry Maven / Gradle / Ivy
/*
* 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 decorator pattern.
*
* Warning: The methods of {@code ForwardingMapEntry} forward
* indiscriminately to the methods of the delegate. For example,
* overriding {@link #getValue} alone will not 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.
*
*
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}.
*
*
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
extends ForwardingObject implements Map.Entry {
// TODO(user): identify places where thread safety is actually lost
/** Constructor for use by subclasses. */
protected ForwardingMapEntry() {}
@Override protected abstract Map.Entry 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
*/
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
*/
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();
}
}