/*
 * Copyright (c) 1996, 2005, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.misc;

import java.util.Enumeration;
import java.util.NoSuchElementException;

Queue: implements a simple queue mechanism. Allows for enumeration of the elements.
Author:Herb Jellinek
/** * Queue: implements a simple queue mechanism. Allows for enumeration of the * elements. * * @author Herb Jellinek */
public class Queue { int length = 0; QueueElement head = null; QueueElement tail = null; public Queue() { }
Enqueue an object.
/** * Enqueue an object. */
public synchronized void enqueue(Object obj) { QueueElement newElt = new QueueElement(obj); if (head == null) { head = newElt; tail = newElt; length = 1; } else { newElt.next = head; head.prev = newElt; head = newElt; length++; } notify(); }
Dequeue the oldest object on the queue. Will wait indefinitely.
Throws:
Returns: the oldest object on the queue.
/** * Dequeue the oldest object on the queue. Will wait indefinitely. * * @return the oldest object on the queue. * @exception java.lang.InterruptedException if any thread has * interrupted this thread. */
public Object dequeue() throws InterruptedException { return dequeue(0L); }
Dequeue the oldest object on the queue.
Params:
  • timeOut – the number of milliseconds to wait for something to arrive.
Throws:
Returns: the oldest object on the queue.
/** * Dequeue the oldest object on the queue. * @param timeOut the number of milliseconds to wait for something * to arrive. * * @return the oldest object on the queue. * @exception java.lang.InterruptedException if any thread has * interrupted this thread. */
public synchronized Object dequeue(long timeOut) throws InterruptedException { while (tail == null) { wait(timeOut); } QueueElement elt = tail; tail = elt.prev; if (tail == null) { head = null; } else { tail.next = null; } length--; return elt.obj; }
Is the queue empty?
Returns:true if the queue is empty.
/** * Is the queue empty? * @return true if the queue is empty. */
public synchronized boolean isEmpty() { return (tail == null); }
Returns an enumeration of the elements in Last-In, First-Out order. Use the Enumeration methods on the returned object to fetch the elements sequentially.
/** * Returns an enumeration of the elements in Last-In, First-Out * order. Use the Enumeration methods on the returned object to * fetch the elements sequentially. */
public final synchronized Enumeration elements() { return new LIFOQueueEnumerator(this); }
Returns an enumeration of the elements in First-In, First-Out order. Use the Enumeration methods on the returned object to fetch the elements sequentially.
/** * Returns an enumeration of the elements in First-In, First-Out * order. Use the Enumeration methods on the returned object to * fetch the elements sequentially. */
public final synchronized Enumeration reverseElements() { return new FIFOQueueEnumerator(this); } public synchronized void dump(String msg) { System.err.println(">> "+msg); System.err.println("["+length+" elt(s); head = "+ (head == null ? "null" : (head.obj)+"")+ " tail = "+(tail == null ? "null" : (tail.obj)+"")); QueueElement cursor = head; QueueElement last = null; while (cursor != null) { System.err.println(" "+cursor); last = cursor; cursor = cursor.next; } if (last != tail) { System.err.println(" tail != last: "+tail+", "+last); } System.err.println("]"); } } final class FIFOQueueEnumerator implements Enumeration { Queue queue; QueueElement cursor; FIFOQueueEnumerator(Queue q) { queue = q; cursor = q.tail; } public boolean hasMoreElements() { return (cursor != null); } public Object nextElement() { synchronized (queue) { if (cursor != null) { QueueElement result = cursor; cursor = cursor.prev; return result.obj; } } throw new NoSuchElementException("FIFOQueueEnumerator"); } } final class LIFOQueueEnumerator implements Enumeration { Queue queue; QueueElement cursor; LIFOQueueEnumerator(Queue q) { queue = q; cursor = q.head; } public boolean hasMoreElements() { return (cursor != null); } public Object nextElement() { synchronized (queue) { if (cursor != null) { QueueElement result = cursor; cursor = cursor.next; return result.obj; } } throw new NoSuchElementException("LIFOQueueEnumerator"); } } class QueueElement { QueueElement next = null; QueueElement prev = null; Object obj = null; QueueElement(Object obj) { this.obj = obj; } public String toString() { return "QueueElement[obj="+obj+(prev == null ? " null" : " prev")+ (next == null ? " null" : " next")+"]"; } }