java - repainting a JPanel and update the screen -

i 'm trying " fade" jpanel using thread . not fading , turning color white black gradually changing rgb values ​​.

public class mostrapainel {      public static void main(string[] args) {         jframe jf = new jframe();         jf.setsize(500, 500);         // centraliza         jf.setlocationrelativeto(null);         painel painel = new painel();         jf.setcontentpane(painel);         jf.setvisible(true);         new thread(painel).start();      } } 

so want repaint panel interval set, panel class

public class painel extends jpanel implements runnable {     // alt+s     /**      * create panel.      */     int cont = 0;      public painel() {         setbackground(color.black);      }      @override     protected void paintcomponent(graphics g) {         if (cont == 1)             super.paintcomponent(g);         graphics2d g2 = (graphics2d) g;          // system.out.println(cont);         g2.setcolor(new color(cont, cont, cont));         int w = getwidth() - 1;         int h = getheight() - 1;         int widthq = w / 8;         int heightq = h / 8;         int size = 0;         int cont = 0;         (int j = heightq; j < getheight(); j += (2 * heightq)) {              (int = size; < getwidth(); += (2 * widthq)) {                 if (cont == 0)                     g2.fillrect(i + widthq, 0, widthq, heightq);                 g2.fillrect(i + widthq, j + heightq, widthq, heightq);                 g2.fillrect(i, j, widthq, heightq);             }             cont++;         }      }      @override     public void run() {         // todo auto-generated method stub         this.cont++;         (cont = 0; cont < 255; cont++) {              if (this.cont < 255) {                 try {                     thread.sleep(50);                 } catch (interruptedexception e) {                     // todo auto-generated catch block                     e.printstacktrace();                 }                 this.repaint();             }         }      }  } 

so paintcomponent() method draw image on panel, , method run() repaint , sum 1 cont variable. work, screen doesn't update every time execute repaint(), fade have low fps. if stay resizing screen fade works well, whats problem?

i solve problem addin line

toolkit.getdefaulttoolkit().sync(); 

thanks help