| /* |
| * 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.GwtCompatible; |
| import java.io.Serializable; |
| |
| /** |
| * 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 |
| */ |
| @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. */ |
| } |