| /* Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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 java.util; |
| |
| /** |
| * AbstractQueue is an abstract class which implements some of the methods in |
| * {@link Queue}. The provided implementations of {@code add, remove} and |
| * {@code element} are based on {@code offer, poll}, and {@code peek} except |
| * that they throw exceptions to indicate some error instead of returning true |
| * or false. |
| * |
| * @param <E> |
| * the type of the element in the collection. |
| */ |
| public abstract class AbstractQueue<E> extends AbstractCollection<E> implements |
| Queue<E> { |
| |
| /** |
| * Constructor to be used by subclasses. |
| */ |
| protected AbstractQueue() { |
| super(); |
| } |
| |
| /** |
| * Adds an element to the queue. |
| * |
| * @param o |
| * the element to be added to the queue. |
| * @return {@code true} if the operation succeeds, otherwise {@code false}. |
| * @throws IllegalStateException |
| * if the element is not allowed to be added to the queue. |
| */ |
| @Override |
| public boolean add(E o) { |
| if (null == o) { |
| throw new NullPointerException(); |
| } |
| if (offer(o)) { |
| return true; |
| } |
| throw new IllegalStateException(); |
| } |
| |
| /** |
| * Adds all the elements of a collection to the queue. If the collection is |
| * the queue itself, then an IllegalArgumentException will be thrown. If |
| * during the process, some runtime exception is thrown, then those elements |
| * in the collection which have already successfully been added will remain |
| * in the queue. The result of the method is undefined if the collection is |
| * modified during the process of the method. |
| * |
| * @param c |
| * the collection to be added to the queue. |
| * @return {@code true} if the operation succeeds, otherwise {@code false}. |
| * @throws NullPointerException |
| * if the collection or any element of it is null. |
| * @throws IllegalArgumentException |
| * If the collection to be added to the queue is the queue |
| * itself. |
| */ |
| @Override |
| public boolean addAll(Collection<? extends E> c) { |
| if (null == c) { |
| throw new NullPointerException(); |
| } |
| if (this == c) { |
| throw new IllegalArgumentException(); |
| } |
| return super.addAll(c); |
| } |
| |
| /** |
| * Removes the element at the head of the queue and returns it. |
| * |
| * @return the element at the head of the queue. |
| * @throws NoSuchElementException |
| * if the queue is empty. |
| */ |
| public E remove() { |
| E o = poll(); |
| if (null == o) { |
| throw new NoSuchElementException(); |
| } |
| return o; |
| } |
| |
| /** |
| * Returns but does not remove the element at the head of the queue. |
| * |
| * @return the element at the head of the queue. |
| * @throws NoSuchElementException |
| * if the queue is empty. |
| */ |
| public E element() { |
| E o = peek(); |
| if (null == o) { |
| throw new NoSuchElementException(); |
| } |
| return o; |
| } |
| |
| /** |
| * Removes all elements of the queue, leaving it empty. |
| */ |
| @Override |
| public void clear() { |
| E o; |
| do { |
| o = poll(); |
| } while (null != o); |
| } |
| } |