/*
    * 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();
   }
 }