使用线程更新Java Applet标签

Question

I have the following Applet class:

public class Marquee extends Applet {
    Label label1 = new Label("Testing");

    public void pushUpdate( String text ) {
        System.out.println( "receiving: " + text );
        label1.setText( text );
        repaint();
    }

    public void init() {
        ScrollText_2 scrollObj = new ScrollText_2( "Applet test" );
        scrollObj.setApplet(this);
        add( label1 );
        scrollObj.run();
    }
}

The ScrollText2 class implements Runnable and has a scroll() method. Right now, all the scroll method does is return the String that the object contains. The run() method of this class looks like this:

while(true) {
    try {
        marquee.pushUpdate( scroll() );
        Thread.sleep( 2000 );
    }
    catch (InterruptedException e) {}
}

The problem is that when I run the applet, if I call the .run() method, then the label on the marquee never displays. I have tried repaint(), just label.setText(), updateUI(), and redraw() to try and get the applet to display the updates but it didn't work.

Any suggestions would be greatly appreciated.

Thank you!

Answer 1

You don't call run() of a Thread or Runnable. You call start() on the Thread or of a Thread that contains the Runnable. Also, you will need to take care to update the GUI components on the GUI's thread. For Swing that means using SwingUtilities.invokeLater(someRunnable) , and I suspect it can be done similarly with AWT.

By the way, why use AWT and not Swing?

Answer 2

You are not creating a new Thread to run scrollObj . When you call scrollObj.run() in Marquee.init() , scrollObj hijacks your applet thread. This means that your main Marquee update loop, which includes paint() , is never reached. Invoking repaint() also does not guarantee that paint() is called. Thus, your Marquee is never painted.

Your code works fine when you replace scrollObj.run(); with

new Thread(scrollObj).start();

Answer 3

marquee example in applet for thread like moving something

import java.applet.*;
import java.awt.*;
/**<applet code="Marquee" height=768 width=1024></applet>*/
public class Marquee extends Applet implements Runnable {
  Color clr[] = { Color.red, Color.green, Color.cyan, Color.blue, Color.orange };
  int xx = 0;
  int x = 100;
  int a = 200;
  Thread t = new Thread(this);

  public void start() {
    t.start();
  }

  public void paint(Graphics g) {
    g.setFont(new Font("Times New Roman", Font.BOLD, 28));
    xx++;
    if (xx == 3) {
      xx = 0;
    }
    g.setColor(clr[xx]);
    g.fillOval(200, 200, x, a);
    g.drawString("Vinay", x, 200);
    g.drawString("Mayur", a, 300);
    x += 1;
    a -= 1;
  }

  public void run() {
    try {
      System.out.println("sdd");
      for (int i = 0; i < 200; i++) {
        Thread.sleep(10);
        repaint();
      }
    } catch (Exception e) {
      System.out.println("Error:-->" + e);
    }
  }
}