Update #0 - First Release

sources/main/java/com/google/common/collect/ForwardingMapEntry.java

@@ -0,0 +1,134 @@
+/*
+ * 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 java.util.Map;
+import java.util.Map.Entry;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.Beta;
+import com.google.common.annotations.GwtCompatible;
+import com.google.common.base.Objects;
+
+/**
+ * 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();
+	}
+}