/* * Copyright (c) 2000 David Flanagan.  All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.thread;/** * This class implements the same API as the Java 1.3 java.util.TimerTask. * Note that a TimerTask can only be scheduled on one Timer at a time, but * that this implementation does not enforce that constraint. **/public abstract class TimerTask implements Runnable {    boolean cancelled = false;    // Has it been cancelled?    long nextTime = -1;           // When is it next scheduled?    long period;                  // What is the execution interval    boolean fixedRate;            // Fixed-rate execution?    protected TimerTask() {}    /**     * Cancel the execution of the task.  Return true if it was actually     * running, or false if it was already cancelled or never scheduled.     **/    public boolean cancel() {	if (cancelled) return false;         // Already cancelled;	cancelled = true;                    // Cancel it	if (nextTime == -1) return false;    // Never scheduled;	return true;    }    /**     * When it the timer scheduled to execute? The run() method can use this     * to see whether it was invoked when it was supposed to be      **/    public long scheduledExecutionTime() { return nextTime; }    /**     * Subclasses must override this to provide that code that is to be run.     * The Timer class will invoke this from its internal thread.     **/    public abstract void run();    // This method is used by Timer to tell the Task how it is scheduled.    void schedule(long nextTime, long period, boolean fixedRate) {	this.nextTime = nextTime;	this.period = period;	this.fixedRate = fixedRate;    }    // This will be called by Timer after Timer calls the run method.    boolean reschedule() {	if (period == 0 || cancelled) return false; // Don't run it again	if (fixedRate) nextTime += period;	else nextTime = System.currentTimeMillis() + period;	return true;    }}