jdk/src/java.base/share/classes/java/util/AbstractQueue.java
author mchung
Fri, 22 May 2015 16:43:39 -0700
changeset 30789 9eca83469588
parent 25859 3317bb8137f4
child 32991 b27c76b82713
permissions -rw-r--r--
8074431: Remove native2ascii tool Reviewed-by: erikj, alanb, okutsu, mfang, naoto
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/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.  Oracle designates this
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 * particular file as subject to the "Classpath" exception as provided
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 * by Oracle in the LICENSE file that accompanied this code.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 */
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/*
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 * This file is available under and governed by the GNU General Public
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 * License version 2 only, as published by the Free Software Foundation.
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 * However, the following notice accompanied the original version of this
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 * file:
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 *
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 * Written by Doug Lea with assistance from members of JCP JSR-166
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 * Expert Group and released to the public domain, as explained at
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 * http://creativecommons.org/publicdomain/zero/1.0/
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 */
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package java.util;
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/**
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 * This class provides skeletal implementations of some {@link Queue}
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 * operations. The implementations in this class are appropriate when
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 * the base implementation does <em>not</em> allow <tt>null</tt>
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 * elements.  Methods {@link #add add}, {@link #remove remove}, and
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 * {@link #element element} are based on {@link #offer offer}, {@link
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 * #poll poll}, and {@link #peek peek}, respectively, but throw
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 * exceptions instead of indicating failure via <tt>false</tt> or
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 * <tt>null</tt> returns.
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 *
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 * <p>A <tt>Queue</tt> implementation that extends this class must
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 * minimally define a method {@link Queue#offer} which does not permit
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 * insertion of <tt>null</tt> elements, along with methods {@link
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 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
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 * {@link Collection#iterator}.  Typically, additional methods will be
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 * overridden as well.  If these requirements cannot be met, consider
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 * instead subclassing {@link AbstractCollection}.
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 *
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 * <p>This class is a member of the
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 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
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 * Java Collections Framework</a>.
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 *
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 * @since 1.5
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 * @author Doug Lea
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 * @param <E> the type of elements held in this collection
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 */
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public abstract class AbstractQueue<E>
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    extends AbstractCollection<E>
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    implements Queue<E> {
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    /**
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     * Constructor for use by subclasses.
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     */
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    protected AbstractQueue() {
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    }
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    /**
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     * Inserts the specified element into this queue if it is possible to do so
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     * immediately without violating capacity restrictions, returning
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     * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt>
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     * if no space is currently available.
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     *
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     * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds,
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     * else throws an <tt>IllegalStateException</tt>.
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     *
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     * @param e the element to add
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     * @return <tt>true</tt> (as specified by {@link Collection#add})
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     * @throws IllegalStateException if the element cannot be added at this
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     *         time due to capacity restrictions
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     * @throws ClassCastException if the class of the specified element
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     *         prevents it from being added to this queue
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     * @throws NullPointerException if the specified element is null and
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     *         this queue does not permit null elements
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     * @throws IllegalArgumentException if some property of this element
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     *         prevents it from being added to this queue
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     */
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    public boolean add(E e) {
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        if (offer(e))
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            return true;
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        else
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            throw new IllegalStateException("Queue full");
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    }
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    /**
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     * Retrieves and removes the head of this queue.  This method differs
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     * from {@link #poll poll} only in that it throws an exception if this
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     * queue is empty.
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     *
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     * <p>This implementation returns the result of <tt>poll</tt>
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     * unless the queue is empty.
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     *
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     * @return the head of this queue
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     * @throws NoSuchElementException if this queue is empty
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     */
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    public E remove() {
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        E x = poll();
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        if (x != null)
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            return x;
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        else
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            throw new NoSuchElementException();
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    }
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    /**
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     * Retrieves, but does not remove, the head of this queue.  This method
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     * differs from {@link #peek peek} only in that it throws an exception if
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     * this queue is empty.
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     *
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     * <p>This implementation returns the result of <tt>peek</tt>
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     * unless the queue is empty.
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     *
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     * @return the head of this queue
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     * @throws NoSuchElementException if this queue is empty
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     */
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    public E element() {
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        E x = peek();
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        if (x != null)
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            return x;
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        else
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            throw new NoSuchElementException();
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    }
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    /**
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     * Removes all of the elements from this queue.
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     * The queue will be empty after this call returns.
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     *
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     * <p>This implementation repeatedly invokes {@link #poll poll} until it
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     * returns <tt>null</tt>.
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     */
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    public void clear() {
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        while (poll() != null)
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            ;
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    }
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    /**
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     * Adds all of the elements in the specified collection to this
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     * queue.  Attempts to addAll of a queue to itself result in
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     * <tt>IllegalArgumentException</tt>. Further, the behavior of
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     * this operation is undefined if the specified collection is
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     * modified while the operation is in progress.
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     *
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     * <p>This implementation iterates over the specified collection,
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     * and adds each element returned by the iterator to this
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     * queue, in turn.  A runtime exception encountered while
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     * trying to add an element (including, in particular, a
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     * <tt>null</tt> element) may result in only some of the elements
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     * having been successfully added when the associated exception is
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     * thrown.
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     *
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     * @param c collection containing elements to be added to this queue
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     * @return <tt>true</tt> if this queue changed as a result of the call
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     * @throws ClassCastException if the class of an element of the specified
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     *         collection prevents it from being added to this queue
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     * @throws NullPointerException if the specified collection contains a
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     *         null element and this queue does not permit null elements,
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     *         or if the specified collection is null
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     * @throws IllegalArgumentException if some property of an element of the
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     *         specified collection prevents it from being added to this
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     *         queue, or if the specified collection is this queue
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     * @throws IllegalStateException if not all the elements can be added at
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     *         this time due to insertion restrictions
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     * @see #add(Object)
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     */
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    public boolean addAll(Collection<? extends E> c) {
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        if (c == null)
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            throw new NullPointerException();
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        if (c == this)
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            throw new IllegalArgumentException();
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        boolean modified = false;
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        for (E e : c)
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            if (add(e))
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                modified = true;
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        return modified;
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    }
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}