Update #0 - First Release

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

@@ -0,0 +1,79 @@
+/*
+ * 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.io.Serializable;
+
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * An abstract base class for implementing the
+ * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
+ * pattern</a>. The {@link #delegate()} method must be overridden to return the
+ * instance being decorated.
+ *
+ * <p>
+ * This class does <i>not</i> forward the {@code hashCode} and {@code equals}
+ * methods through to the backing object, but relies on {@code Object}'s
+ * implementation. This is necessary to preserve the symmetry of {@code equals}.
+ * Custom definitions of equality are usually based on an interface, such as
+ * {@code Set} or {@code List}, so that the implementation of {@code equals} can
+ * cast the object being tested for equality to the custom interface. {@code
+ * ForwardingObject} implements no such custom interfaces directly; they are
+ * implemented only in subclasses. Therefore, forwarding {@code equals} would
+ * break symmetry, as the forwarding object might consider itself equal to the
+ * object being tested, but the reverse could not be true. This behavior is
+ * consistent with the JDK's collection wrappers, such as
+ * {@link java.util.Collections#unmodifiableCollection}. Use an
+ * interface-specific subclass of {@code ForwardingObject}, such as
+ * {@link ForwardingList}, to preserve equality behavior, or override
+ * {@code equals} directly.
+ *
+ * <p>
+ * The {@code toString} method is forwarded to the delegate. Although this class
+ * does not implement {@link Serializable}, a serializable subclass may be
+ * created since this class has a parameter-less constructor.
+ *
+ * @author Mike Bostock
+ * @since 2.0 (imported from Google Collections Library)
+ */
+@GwtCompatible
+public abstract class ForwardingObject {
+
+	/** Constructor for use by subclasses. */
+	protected ForwardingObject() {
+	}
+
+	/**
+	 * Returns the backing delegate instance that methods are forwarded to. Abstract
+	 * subclasses generally override this method with an abstract method that has a
+	 * more specific return type, such as {@link ForwardingSet#delegate}. Concrete
+	 * subclasses override this method to supply the instance being decorated.
+	 */
+	protected abstract Object delegate();
+
+	/**
+	 * Returns the string representation generated by the delegate's
+	 * {@code toString} method.
+	 */
+	@Override
+	public String toString() {
+		return delegate().toString();
+	}
+
+	/* No equals or hashCode. See class comments for details. */
+}