swing - Java run+repaint = grey window -

i'm trying play around jframe/jpanels repaint(); , forth, when start thread, , call repaint via run while true, spits out line of system.out.println("as"); put in place check if loop running.

so question is: why drawings disappearing when calling repaint in loop? (it seems jframe canvas_width/height showing up, no panels etc.)

public static void main(string[] args) {      jframe frame = new jframe();     frame.setsize(canvas_width, canvas_height);     frame.setpreferredsize(new dimension(canvas_width, canvas_height));     frame.setvisible(true);     frame.setresizable(false);     frame.setdefaultcloseoperation(jframe.exit_on_close);     jpanel p = new jpanel(new gridlayout());      frame.getcontentpane().add(p);     s = new something();      p.add(s);     p.setbackground(color.black);     frame.pack();  } 

and class:

public class extends jpanel implements runnable {   public something(){     thread t = new thread();     t.start();     run();  }   @override public void paintcomponent(graphics g){     super.paintcomponent(g);     g.setcolor(color.cyan);     g.fillrect(0, 0, getwidth()-150, getheight()-100);     g.setcolor(color.black);     g.filloval(10, 10, 25, 25);  }   @override public void run() {     while(true){     repaint();     system.out.println("as");      try {         thread.sleep(1);     } catch (interruptedexception e){}     } } } 

any regarding contentpane appreciated, since, i'm not sure done correctly.

instead of calling thread.sleep(n) in thread, implement swing timer repeating tasks. ensures repaint() called on event dispatch thread.

see concurrency in swing more details.

also, repainting every 1 millisecond being optimistic.

working sscce e.g. (note version changes co-ords of resulting paint operations, know happening!

import java.awt.*; import java.awt.event.*; import javax.swing.*;  public class extends jpanel {      static final int canvas_width = 400;     static final int canvas_height = 100;     private int xdelta = 0;  public something(){     actionlistener animater = new actionlistener() {         @override         public void actionperformed(actionevent ae) {             repaint();         }     };     timer t = new timer(10,animater);     t.start(); }   @override public void paintcomponent(graphics g){     super.paintcomponent(g);     g.setcolor(color.cyan);     g.fillrect(0, 0, getwidth()-(xdelta--), getheight()-100);     g.setcolor(color.black);     g.filloval(xdelta, 10, 25, 25);      if (xdelta<0) {         xdelta = canvas_width;     } }  @override public dimension getpreferredsize() {     return new dimension(canvas_width, canvas_height); }  public static void main(string[] args) {      jframe frame = new jframe();      frame.setdefaultcloseoperation(jframe.exit_on_close);     jpanel p = new jpanel(new gridlayout());      frame.getcontentpane().add(p);     s = new something();      p.add(s);     p.setbackground(color.black);     frame.pack();     frame.setresizable(false);     frame.setvisible(true); } }