    001    /*
    002     * Copyright (C) 2007 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.collect;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.annotations.GwtCompatible;
    021    import com.google.common.base.Objects;
    022
    023    import java.util.Map;
    024    import java.util.Map.Entry;
    025
    026    import javax.annotation.Nullable;
    027
    028    /**
    029     * A map entry which forwards all its method calls to another map entry.
    030     * Subclasses should override one or more methods to modify the behavior of the
    031     * backing map entry as desired per the <a
    032     * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
    033     *
    034     * <p><i>Warning:</i> The methods of {@code ForwardingMapEntry} forward
    035     * <i>indiscriminately</i> to the methods of the delegate. For example,
    036     * overriding {@link #getValue} alone <i>will not</i> change the behavior of
    037     * {@link #equals}, which can lead to unexpected behavior. In this case, you
    038     * should override {@code equals} as well, either providing your own
    039     * implementation, or delegating to the provided {@code standardEquals} method.
    040     *
    041     * <p>Each of the {@code standard} methods, where appropriate, use {@link
    042     * Objects#equal} to test equality for both keys and values. This may not be
    043     * the desired behavior for map implementations that use non-standard notions of
    044     * key equality, such as the entry of a {@code SortedMap} whose comparator is
    045     * not consistent with {@code equals}.
    046     *
    047     * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
    048     * when all of the methods that they depend on are thread-safe.
    049     *
    050     * @author Mike Bostock
    051     * @author Louis Wasserman
    052     * @since 2.0 (imported from Google Collections Library)
    053     */
    054    @GwtCompatible
    055    public abstract class ForwardingMapEntry<K, V>
    056        extends ForwardingObject implements Map.Entry<K, V> {
    057      // TODO(user): identify places where thread safety is actually lost
    058
    059      /** Constructor for use by subclasses. */
    060      protected ForwardingMapEntry() {}
    061
    062      @Override protected abstract Map.Entry<K, V> delegate();
    063
    064      @Override
    065      public K getKey() {
    066        return delegate().getKey();
    067      }
    068
    069      @Override
    070      public V getValue() {
    071        return delegate().getValue();
    072      }
    073
    074      @Override
    075      public V setValue(V value) {
    076        return delegate().setValue(value);
    077      }
    078
    079      @Override public boolean equals(@Nullable Object object) {
    080        return delegate().equals(object);
    081      }
    082
    083      @Override public int hashCode() {
    084        return delegate().hashCode();
    085      }
    086
    087      /**
    088       * A sensible definition of {@link #equals(Object)} in terms of {@link
    089       * #getKey()} and {@link #getValue()}. If you override either of these
    090       * methods, you may wish to override {@link #equals(Object)} to forward to
    091       * this implementation.
    092       *
    093       * @since 7.0
    094       */
    095      @Beta protected boolean standardEquals(@Nullable Object object) {
    096        if (object instanceof Entry) {
    097          Entry<?, ?> that = (Entry<?, ?>) object;
    098          return Objects.equal(this.getKey(), that.getKey())
    099              && Objects.equal(this.getValue(), that.getValue());
    100        }
    101        return false;
    102      }
    103
    104      /**
    105       * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()}
    106       * and {@link #getValue()}. If you override either of these methods, you may
    107       * wish to override {@link #hashCode()} to forward to this implementation.
    108       *
    109       * @since 7.0
    110       */
    111      @Beta protected int standardHashCode() {
    112        K k = getKey();
    113        V v = getValue();
    114        return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
    115      }
    116
    117      /**
    118       * A sensible definition of {@link #toString} in terms of {@link
    119       * #getKey} and {@link #getValue}. If you override either of these
    120       * methods, you may wish to override {@link #equals} to forward to this
    121       * implementation.
    122       *
    123       * @since 7.0
    124       */
    125      @Beta protected String standardToString() {
    126        return getKey() + "=" + getValue();
    127      }
    128    }