127 lines
3.3 KiB
Java
127 lines
3.3 KiB
Java
/*
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* Copyright (C) 2007 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import java.util.NoSuchElementException;
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import java.util.Queue;
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import com.google.common.annotations.GwtCompatible;
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/**
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* A queue which forwards all its method calls to another queue. Subclasses
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* should override one or more methods to modify the behavior of the backing
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* queue as desired per the
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* <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
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* pattern</a>.
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*
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* <p>
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* <b>Warning:</b> The methods of {@code ForwardingQueue} forward
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* <b>indiscriminately</b> to the methods of the delegate. For example,
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* overriding {@link #add} alone <b>will not</b> change the behavior of
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* {@link #offer} which can lead to unexpected behavior. In this case, you
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* should override {@code offer} as well, either providing your own
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* implementation, or delegating to the provided {@code standardOffer} method.
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*
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* <p>
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* The {@code standard} methods are not guaranteed to be thread-safe, even when
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* all of the methods that they depend on are thread-safe.
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*
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* @author Mike Bostock
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* @author Louis Wasserman
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible
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public abstract class ForwardingQueue<E> extends ForwardingCollection<E> implements Queue<E> {
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/** Constructor for use by subclasses. */
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protected ForwardingQueue() {
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}
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@Override
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protected abstract Queue<E> delegate();
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@Override
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public boolean offer(E o) {
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return delegate().offer(o);
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}
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@Override
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public E poll() {
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return delegate().poll();
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}
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@Override
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public E remove() {
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return delegate().remove();
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}
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@Override
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public E peek() {
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return delegate().peek();
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}
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@Override
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public E element() {
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return delegate().element();
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}
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/**
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* A sensible definition of {@link #offer} in terms of {@link #add}. If you
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* override {@link #add}, you may wish to override {@link #offer} to forward to
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* this implementation.
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*
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* @since 7.0
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*/
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protected boolean standardOffer(E e) {
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try {
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return add(e);
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} catch (IllegalStateException caught) {
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return false;
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}
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}
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/**
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* A sensible definition of {@link #peek} in terms of {@link #element}. If you
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* override {@link #element}, you may wish to override {@link #peek} to forward
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* to this implementation.
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*
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* @since 7.0
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*/
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protected E standardPeek() {
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try {
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return element();
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} catch (NoSuchElementException caught) {
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return null;
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}
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}
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/**
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* A sensible definition of {@link #poll} in terms of {@link #remove}. If you
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* override {@link #remove}, you may wish to override {@link #poll} to forward
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* to this implementation.
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*
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* @since 7.0
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*/
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protected E standardPoll() {
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try {
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return remove();
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} catch (NoSuchElementException caught) {
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return null;
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}
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}
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}
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