/*
 * 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 org.checkerframework.checker.nullness.qual.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 ForwardingMapEntry forward indiscriminately to the methods of the delegate. For example, overriding getValue alone will not change the behavior of equals, which can lead to unexpected behavior. In this case, you should override equals as well, either providing your own implementation, or delegating to the provided standardEquals method. 
Each of the standard methods, where appropriate, use 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 SortedMap whose comparator is not consistent with equals. 
The 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, Louis Wasserman
Since:
2.0/**
 * 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><b>Warning:</b> 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
 */
@GwtCompatible
public abstract class ForwardingMapEntry<K, V> extends ForwardingObject implements Map.Entry<K, V> {
  // TODO(lowasser): identify places where thread safety is actually lost

  
Constructor for use by subclasses. /** Constructor for use by subclasses. */
  protected ForwardingMapEntry() {}

  @Override
  protected abstract 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 equals(Object) in terms of getKey() and getValue(). If you override either of these methods, you may wish to override equals(Object) to forward to this implementation. 
Since:
7.0/**
   * 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 hashCode() in terms of getKey() and getValue(). If you override either of these methods, you may wish to override hashCode() to forward to this implementation. 
Since:
7.0/**
   * 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 ForwardingObject.toString in terms of getKey and getValue. If you override either of these methods, you may wish to override equals to forward to this implementation. 
Since:
7.0/**
   * 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();
  }
}