/*
* 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
*/
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();
}
}