/*
 * Copyright (C) 2007 Google Inc.
 *
 * 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.base.Objects;

import java.util.Map.Entry;

/**
 * Implementation of the {@code equals}, {@code hashCode}, and {@code toString}
 * methods of {@code Entry}.
 *
 * @author Jared Levy
 */
public abstract class AbstractMapEntry<K, V> implements Entry<K, V> {

  public abstract K getKey();

  public abstract V getValue();

  /**
   * {@inheritDoc}
   *
   * <p>This implementation throws an {@link UnsupportedOperationException}.
   * Override this method to support mutable map entries.
   */
  public V setValue(V value) {
    throw new UnsupportedOperationException();
  }

  /**
   * Indicates whether an object equals this entry, following the behavior
   * specified in {@link Entry#equals}.
   */
  @Override public boolean equals(Object o) {
    if (o == this) {
      return true;
    }
    if (!(o instanceof Entry<?, ?>)) {
      return false;
    }
    Entry<?, ?> e = (Entry<?, ?>) o;
    return Objects.equal(e.getKey(), getKey())
        && Objects.equal(e.getValue(), getValue());
  }

  /**
   * Return this entry's hash code, following the behavior specified in
   * {@link Entry#hashCode}.
   */
  @Override public int hashCode() {
    K k = getKey();
    V v = getValue();
    return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
  }

  /**
   * Returns a string representation of the form <code>{key}={value}</code>.
   */
  @Override public String toString() {
    return getKey() + "=" + getValue();
  }
}