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.GwtCompatible; 201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.NoSuchElementException; 221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.Queue; 231d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 241d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/** 251d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A queue which forwards all its method calls to another queue. Subclasses 261d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * should override one or more methods to modify the behavior of the backing 271d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * queue as desired per the <a 281d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 291d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 301d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p><b>Warning:</b> The methods of {@code ForwardingQueue} forward 311d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <b>indiscriminately</b> to the methods of the delegate. For example, 321d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * overriding {@link #add} alone <b>will not</b> change the behavior of {@link 331d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * #offer} which can lead to unexpected behavior. In this case, you should 341d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@code offer} as well, either providing your own implementation, or 351d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * delegating to the provided {@code standardOffer} method. 361d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 371d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p>The {@code standard} methods are not guaranteed to be thread-safe, even 381d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * when all of the methods that they depend on are thread-safe. 391d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 401d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Mike Bostock 411d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Louis Wasserman 421d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 2.0 (imported from Google Collections Library) 431d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 441d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert@GwtCompatible 450888a09821a98ac0680fad765217302858e70fa4Paul Duffinpublic abstract class ForwardingQueue<E> extends ForwardingCollection<E> 460888a09821a98ac0680fad765217302858e70fa4Paul Duffin implements Queue<E> { 471d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 481d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** Constructor for use by subclasses. */ 491d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert protected ForwardingQueue() {} 501d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 510888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override protected abstract Queue<E> delegate(); 527dd252788645e940eada959bdde927426e2531c9Paul Duffin 530888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 541d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public boolean offer(E o) { 551d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().offer(o); 561d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 571d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 580888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 591d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E poll() { 601d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().poll(); 611d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 621d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 630888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 641d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E remove() { 651d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().remove(); 661d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 671d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 680888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 691d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E peek() { 701d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().peek(); 711d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 721d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 730888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 741d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public E element() { 751d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return delegate().element(); 761d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 771d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 781d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 791d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #offer} in terms of {@link #add}. If you 801d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #add}, you may wish to override {@link #offer} to forward 811d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * to this implementation. 821d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 831d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 841d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 857dd252788645e940eada959bdde927426e2531c9Paul Duffin protected boolean standardOffer(E e) { 861d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 871d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return add(e); 881d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (IllegalStateException caught) { 891d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return false; 901d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 911d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 921d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 931d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 941d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #peek} in terms of {@link #element}. If you 951d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #element}, you may wish to override {@link #peek} to 961d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * forward to this implementation. 971d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 981d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 991d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 1007dd252788645e940eada959bdde927426e2531c9Paul Duffin protected E standardPeek() { 1011d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 1021d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return element(); 1031d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (NoSuchElementException caught) { 1041d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return null; 1051d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1061d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1071d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 1081d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 1091d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * A sensible definition of {@link #poll} in terms of {@link #remove}. If you 1101d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * override {@link #remove}, you may wish to override {@link #poll} to forward 1111d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * to this implementation. 1121d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 1131d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 7.0 1141d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 1157dd252788645e940eada959bdde927426e2531c9Paul Duffin protected E standardPoll() { 1161d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 1171d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return remove(); 1181d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } catch (NoSuchElementException caught) { 1191d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return null; 1201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 1221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert} 123