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canvas repaint

Posted on 1999-01-21
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Last Modified: 2011-09-20
I have an applet with a class "Square" that extends canvas.
Below is an example of my code :

private Square square;
private TextArea textarea;

public void init () {
     textarea = new TextArea();
     square = new Square();
}

.....   //other codes
.....

public void repaintingCanvas() {
        textarea.append ("testing");       //line 1
        square.repaint();                  //line 2  
        textarea.append ("after testing"); //line 3
        }    


How come I will be able to see the execution of line 1 and line 3 first before seeing the execution of line 2. I tried to "sleep" the applet after line 2, hoping to see the effect of square.repaint()incase it takes time to repaint, but it will still sleep then I can see the words "after testing" in textarea (execution of line 3) and only later will I see the effect of repaint() of the particular canvas.

 Why is this so, is it because I am not optimizing my codes properly or because all directions of applet will be executed first and execution of canvas is done later.

fyi....applet implements runnable

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Question by:caphey
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Accepted Solution

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heyhey_ earned 100 total points
ID: 1234475
painting is usually done in another Thread (probably the standard event Thread) so:

- when you call repaint() you just make request for repainting, which may be server some time later.
- when you call repaint from the code that is triggered from some  Event (for example actionPerformed() of a Button) you are working INSIDE the event Thread, so paining (and all other events propagation) will be BLOCKED until you quit the event handler method. sleep() won't help too.

it a standard practice to place all the 'heavy' code inside another Thread, so that you don't block the system event&paint Thread.

if you need more help, you'd better post a small example that reproduces yout problem.

best regards
  heyhey

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