Problem with Thread.sleep(x) in a for loop - Java

I'm making a frame which contains a round rectangle. This rectangle is constantly (re)painting itself with smaller values.

The plan is, First the rectangle decreases in width(x), after that the rectangle decreases in height(y).

But for now I just want to get the width decreasing done with. But I'm having troubles here already.

Please note, i'm only drawing the rectangle's borders, so I don't want to fill it.

I made a for loop as follows:

 for (rectWidth = 470; rectWidth >= 0; --rectWidth) {

           try {
                //simply made to represent rectWidth's value, not really relevant
                System.out.println("rectWidth is: " + rectWidth);

                //draw the rectangle with it's new width, ignore the "rectHeight" for now.
                g.drawRoundRect(5, 5, rectWidth, rectHeight, 10, 10);

                //this Thread.sleep is messing up my frame which has an instance of this class added 
                //to it also, my program is uninterruptable when adding this Thread.sleep
                Thread.sleep(500);

            } catch (Exception ex) {
                //rectangle's value will be returned here when interrupted.

          }
         }

My que开发者_JS百科stion is, how can I add a 'sleep' in my for loop in order to make the drawing not go all too fast, withouth messing my frame. This thread.sleep is messing my frame up in a way that I don't even see the rectangle anymore.

I want to achieve a smooth (re)painting of the rectangle. (And yes I know as this piece of code is now it isn't repainting the rectangle but constantly painting a slightly smaller rectangle in the frame.)

The reason that the rectangle isn't getting displayed is that the display is updated on the EventDispatchThread which is probably the same one your loop is on. That is it can't paint the rectangle because it's too busy sleeping.

The solution is to use a Swing Timer which will run and happily sleep sending tasks to the EventDispatchThread when updating.

Also you can start drawing thread

@Override
public void run(){
  while(shouldDraw())
  this.wait(500);

  yourCalculations(); // maybe setting fields in runnable object

  SwingUtilities.invokeAndWait(yourRunnableObject); // or invokeLater if you prefer non blocking version
  }

This code shows only conception (I've skipped synchronization and exception handling). SwingTimer looks more elegant but I've never used it.