Thread.sleep in while loop

[oaieuy]

Could somebody explain me, why that short midlet doesn’t work as it should.

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

public class Abcdef extends MIDlet implements CommandListener {
    private Command exitCommand;
    private Form dataViewForm;
    int x;
    public Abcdef() {
		dataViewForm = new Form("Serial Data Viewer");
        exitCommand = new Command("Exit", Command.EXIT, 1);
        dataViewForm.addCommand(exitCommand);
        dataViewForm.setCommandListener(this);
        for(x=0;x<10;x++){
        	dataViewForm.append("ABCDEFGH \n");
        	System.out.println("ABCDEFGH");
        	try{
           		Thread.sleep(1000);
        	}catch(InterruptedException e){}  
    	}
    }
    protected void startApp() {
        Display.getDisplay(this).setCurrent(dataViewForm);
    }

    protected void pauseApp() {}
    protected void destroyApp(boolean bool) {}

    public void commandAction(Command cmd, Displayable disp) {
        if (cmd == exitCommand) {
            destroyApp(false);
            notifyDestroyed();
        }
    }
}

The result should looks like this:

ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH
// 1 sec. Pause
ABCDEFGH

But the result is:

//10 sec. Pause
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH
ABCDEFGH

On the console WTK result is ok, but on emulator WTK result isn’t ok.

[grahamhughes]

Yup. Your expectation of what it should do is not correct.

You have the loop in the constructor. Nothing will appear, because you haven't displayed the form yet. By the time startApp() is called, you have already added all the strings to the form, so it appears in its final state.

Avoid putting any code in the MIDlet constructor.

Also, avoid putting time-consuming code in startApp(). startApp() is an event, and is delivered through the event queue. The event queue delivers only one event at a time, so until an event method (like startApp()) returns, no other event will be delivered. The display is updated by events, so if you block startApp() from returning, nothing will be displayed.

Here's a modified version:

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

public class Abcdef extends MIDlet implements CommandListener, Runnable {
    private Command exitCommand;
    private Form dataViewForm;

    protected void startApp() {
        // this is important to stop the code from executing more than once
        if (dataViewForm == null) {
            // this is moved from the constructor
            dataViewForm = new Form("Serial Data Viewer");
            exitCommand = new Command("Exit", Command.EXIT, 1);
            dataViewForm.addCommand(exitCommand);
            dataViewForm.setCommandListener(this);

            // start a thread to perform the loop
            (new Thread(this)).start();
        }

        Display.getDisplay(this).setCurrent(dataViewForm);
    }

    protected void pauseApp() {
        // do nothing
    }

    protected void destroyApp(boolean mustExit) {
        // do nothing
    }

    public void commandAction(Command cmd, Displayable disp) {
        if (cmd == exitCommand) {
            destroyApp(false);
            notifyDestroyed();
        }
    }

    public void run() {
        for (int x = 0; x < 10; x++) {
            dataViewForm.append("ABCDEFGH \n");
            System.out.println("ABCDEFGH");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // ignore
            }  
    	}
    }
}

Graham.

[oaieuy]

very very thank You