| /* |
| * 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 com.google.errorprone.annotations.CanIgnoreReturnValue; |
| import java.util.NoSuchElementException; |
| import java.util.Queue; |
| |
| /** |
| * A queue which forwards all its method calls to another queue. Subclasses should override one or |
| * more methods to modify the behavior of the backing queue as desired per the <a |
| * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. |
| * |
| * <p><b>Warning:</b> The methods of {@code ForwardingQueue} forward <b>indiscriminately</b> to the |
| * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the |
| * behavior of {@link #offer} which can lead to unexpected behavior. In this case, you should |
| * override {@code offer} as well, either providing your own implementation, or delegating to the |
| * provided {@code standardOffer} method. |
| * |
| * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code |
| * default} methods. Instead, it inherits their default implementations. When those implementations |
| * invoke methods, they invoke methods on the {@code ForwardingQueue}. |
| * |
| * <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 |
| */ |
| @GwtCompatible |
| public abstract class ForwardingQueue<E> extends ForwardingCollection<E> implements Queue<E> { |
| |
| /** Constructor for use by subclasses. */ |
| protected ForwardingQueue() {} |
| |
| @Override |
| protected abstract Queue<E> delegate(); |
| |
| @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this? |
| @Override |
| public boolean offer(E o) { |
| return delegate().offer(o); |
| } |
| |
| @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this? |
| @Override |
| public E poll() { |
| return delegate().poll(); |
| } |
| |
| @CanIgnoreReturnValue |
| @Override |
| public E remove() { |
| return delegate().remove(); |
| } |
| |
| @Override |
| public E peek() { |
| return delegate().peek(); |
| } |
| |
| @Override |
| public E element() { |
| return delegate().element(); |
| } |
| |
| /** |
| * A sensible definition of {@link #offer} in terms of {@link #add}. If you override {@link #add}, |
| * you may wish to override {@link #offer} to forward to this implementation. |
| * |
| * @since 7.0 |
| */ |
| protected boolean standardOffer(E e) { |
| try { |
| return add(e); |
| } catch (IllegalStateException caught) { |
| return false; |
| } |
| } |
| |
| /** |
| * A sensible definition of {@link #peek} in terms of {@link #element}. If you override {@link |
| * #element}, you may wish to override {@link #peek} to forward to this implementation. |
| * |
| * @since 7.0 |
| */ |
| protected E standardPeek() { |
| try { |
| return element(); |
| } catch (NoSuchElementException caught) { |
| return null; |
| } |
| } |
| |
| /** |
| * A sensible definition of {@link #poll} in terms of {@link #remove}. If you override {@link |
| * #remove}, you may wish to override {@link #poll} to forward to this implementation. |
| * |
| * @since 7.0 |
| */ |
| protected E standardPoll() { |
| try { |
| return remove(); |
| } catch (NoSuchElementException caught) { |
| return null; |
| } |
| } |
| } |