Programming Tutorials

Timer and TimerTask example in J2ME

By: Emiley J. in J2ME Tutorials on 2008-07-07  

This sample J2ME program demonstrates the use of Timer and TimerTask in a midlet. This MIDlet creates two gauges. One gauge gaugeOne,  sets elements from low to high. The other, gaugeTwo, set elements from high to low. In effect, this has gaugeOne "going up", and gaugeTwo "going down."

The two timers fire at different intervals.
 
There are two commands on our form:

1. OK: toggles whether the times are active or not.
2. EXIT: exits the MIDlet.
   
   

/*
 * Copyright (c) 2000-2001 Sun Microsystems, Inc. All Rights Reserved.
 */

import java.lang.*;
import java.io.*;
import java.util.*;

import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

public class TimerMIDlet extends MIDlet implements CommandListener {
    // number of elements in gauge
    final private static int GAUGE_MAX = 10;

    private boolean timersRunning; // tracks state of timers
    private Display myDisplay;     // handle to the display

    private Gauge gaugeOne;        // "going up" gauge
    private Gauge gaugeTwo;        // "going down" gauge

    private Form myScreen;         // form on which to 
                                   // place gauges
    private Command cmdOK;         // OK command
    private Command cmdExit;       // EXIT command

    private Timer timer;
    private MyTimerTask timerTaskOne;
    private MyTimerTask timerTaskTwo;

    /**
     * Internal class that provides a TimerTask.
     */
    private class MyTimerTask extends TimerTask {
        private Gauge myGauge; // reference to gauge
        private boolean goUp;  // if true, go up
        private int num;       // number of times called

        /**
         * Public constructor: stores "direction" and a reference to
         * a gauge.
         */
        public MyTimerTask(Gauge g, boolean up) {
            myGauge = g;
            goUp = up;
        }

        /**
         * As the timer fires, this method is invoked. Set gauge
         * based on goUp
         */
        public void run() {
            num++;
            myGauge.setValue(goUp ?
                             GAUGE_MAX -(num % GAUGE_MAX) :
                             num % GAUGE_MAX);
        }
    }

    /**
     * Public constructor: gets handle to display,
     * creates form, gauges, and commands.
     */
    public TimerMIDlet() {
        myDisplay = Display.getDisplay(this);
        myScreen = new Form("TimerMIDlet");
        gaugeOne = new Gauge("Up Gauge",
                             false,
                             GAUGE_MAX,
                             0);
        myScreen.append(gaugeOne);

        gaugeTwo = new Gauge("Down Gauge",
                             false,
                             GAUGE_MAX,
                             GAUGE_MAX);
        myScreen.append(gaugeTwo);

        cmdOK = new Command("OK", Command.OK, 1);
        cmdExit = new Command("Exit", Command.EXIT, 1);
        myScreen.addCommand(cmdOK);
        myScreen.addCommand(cmdExit);
        myScreen.setCommandListener(this);
    }

    /**
     * Changes the state of timers to/from active to/from
     * not-active.
     */
    private void flipFlop() {
        if (timersRunning) {
            timerTaskOne.cancel();
            timerTaskTwo.cancel();
            timer.cancel();
            timersRunning = false;
        } else {
            timer = new Timer();
            timerTaskOne = new MyTimerTask(gaugeOne, false);
            timerTaskTwo = new MyTimerTask(gaugeTwo, true);
            timer.schedule(timerTaskOne, 0, 1000);
            timer.schedule(timerTaskTwo, 0, 1500);
            timersRunning = true;
        }
    }

    /**
     * Called by the system to start our MIDlet.
    * @exception MIDletStateChangeException
     */
    protected void startApp() throws MIDletStateChangeException {
        myDisplay.setCurrent(myScreen);
        flipFlop();
    }

    /**
     * Called by the system to pause our MIDlet.
     * No actions required by our MIDLet.
     */
    protected void pauseApp() {}

    /**
     * Called by the system to end our MIDlet.
     * No actions required by our MIDLet.
     */
    protected void destroyApp(boolean unconditional) {}

    /***
     * Respond to command selections. Process two commands:
     * 
     * OK: flip flop the timers to/from active
     * EXIT: exit this MIDlet
     * 
     */
    public void commandAction(Command c, Displayable d) {
        if (c == cmdOK) {
            flipFlop();
        } else if (c == cmdExit) {
            destroyApp(false);
            notifyDestroyed();
        }
    }
}