11d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/* 21d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Copyright (C) 2007 The Guava Authors 31d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 41d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Licensed under the Apache License, Version 2.0 (the "License"); 51d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * you may not use this file except in compliance with the License. 61d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * You may obtain a copy of the License at 71d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 81d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * http://www.apache.org/licenses/LICENSE-2.0 91d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 101d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Unless required by applicable law or agreed to in writing, software 111d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * distributed under the License is distributed on an "AS IS" BASIS, 121d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 131d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * See the License for the specific language governing permissions and 141d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * limitations under the License. 151d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 161d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 171d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertpackage com.google.common.collect; 181d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 191d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport com.google.common.annotations.Beta; 201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport com.google.common.annotations.GwtCompatible; 211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.NoSuchElementException; 231d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.Queue; 241d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 251d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/** 261d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A queue which forwards all its method calls to another queue. Subclasses 271d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * should override one or more methods to modify the behavior of the backing 281d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * queue as desired per the <a 291d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 301d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 311d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p><b>Warning:</b> The methods of {@code ForwardingQueue} forward 321d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <b>indiscriminately</b> to the methods of the delegate. For example, 331d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * overriding {@link #add} alone <b>will not</b> change the behavior of {@link 341d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * #offer} which can lead to unexpected behavior. In this case, you should 351d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@code offer} as well, either providing your own implementation, or 361d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * delegating to the provided {@code standardOffer} method. 371d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 381d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p>The {@code standard} methods are not guaranteed to be thread-safe, even 391d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * when all of the methods that they depend on are thread-safe. 401d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 411d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Mike Bostock 421d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Louis Wasserman 431d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 2.0 (imported from Google Collections Library) 441d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 451d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert@GwtCompatible 461d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertpublic abstract class ForwardingQueue<E> extends ForwardingCollection<E> 471d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert implements Queue<E> { 481d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 491d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** Constructor for use by subclasses. */ 501d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert protected ForwardingQueue() {} 511d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 521d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override protected abstract Queue<E> delegate(); 531d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 541d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 551d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public boolean offer(E o) { 561d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().offer(o); 571d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 581d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 591d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 601d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E poll() { 611d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().poll(); 621d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 631d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 641d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 651d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E remove() { 661d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().remove(); 671d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 681d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 691d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 701d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E peek() { 711d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().peek(); 721d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 731d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 741d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 751d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E element() { 761d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().element(); 771d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 781d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 791d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 801d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #offer} in terms of {@link #add}. If you 811d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #add}, you may wish to override {@link #offer} to forward 821d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * to this implementation. 831d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 841d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 851d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 861d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Beta protected boolean standardOffer(E e) { 871d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 881d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return add(e); 891d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (IllegalStateException caught) { 901d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return false; 911d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 921d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 931d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 941d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 951d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #peek} in terms of {@link #element}. If you 961d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #element}, you may wish to override {@link #peek} to 971d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * forward to this implementation. 981d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 991d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 1001d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 1011d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Beta protected E standardPeek() { 1021d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 1031d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return element(); 1041d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (NoSuchElementException caught) { 1051d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return null; 1061d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1071d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1081d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 1091d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 1101d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #poll} in terms of {@link #remove}. If you 1111d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #remove}, you may wish to override {@link #poll} to forward 1121d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * to this implementation. 1131d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 1141d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 1151d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 1161d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Beta protected E standardPoll() { 1171d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 1181d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return remove(); 1191d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (NoSuchElementException caught) { 1201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return null; 1211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1231d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert} 124