update() gets never called

[flok]

Hi,

From what I understand at java.sun.com/products/jfc/tsc/articles/painting/ , repaint() lets awt call update(). But what you can see with the following code, what gets called is paint()! Am I doing something wrong? What?
Thanks.

import java.awt.*;
import javax.swing.*;

public class pu extends JFrame
{
	public void paint(Graphics g)
	{
		System.out.println("paint");
	}

	public void update(Graphics g)
	{
		System.out.println("update");
	}

	public static void main(String[] arg)
	{
		try
		{
			/* retrieve max window size */
			GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
			GraphicsDevice[] gs = ge.getScreenDevices();
			GraphicsConfiguration [] gc = gs[0].getConfigurations();
			Rectangle r = gc[0].getBounds();

			/* create frame to draw in */
			pu frame = new pu();
			frame.setSize(r.width, r.height);

			System.out.println("set visible");
			frame.setVisible(true);

			for(;;)
			{
				System.out.println("Invoke repaint");

				frame.repaint();

				System.out.println("Sleep");

				Thread.sleep(1000);
			}
		}
		catch(Exception e)
		{
			System.out.println("exception " + e);
		}
	}
}

[Willi]

I think if you want to draw a string on a frame by using paint() method, you must use the drawString() method of class Graphics.

[flok]

I think if you want to draw a string on a frame by using paint() method, you must use the drawString() method of class Graphics.

No. That is also not the point of my question.

What I mean is: repaint() should let AWT call update() but in reality it calls paint(). Why is that? The System.out.println()'s are only debugging calls to show what is going on and wrong.

[Willi]

the method repaint() will call paint() method because you are using a lightweight (Swing) component. Try a heavyweight component (AWT) instead. I think it works!

[flok]

the method repaint() will call paint() method because you are using a lightweight (Swing) component. Try a heavyweight component (AWT) instead. I think it works!

Yes it does! Thanks a lot!

I replaced JFrame by Frame and now I get updates.

[Willi]

You are welcome!

Anyway, do you have the JDK Documentation with you? If not, download one here. It is the best reference for all programmers.

[Fubarable]

But I don't understand why it is important that update gets called here. All update does in swing is call paint(), something which repaint already does (indirectly). I will posit that regardless you are far better off using Swing and its lightweight components, that there is a better way of solving whatever underlying problem you are having that makes you feel impelled to override update().

[flok]

But I don't understand why it is important that update gets called here. All update does in swing is call paint(), something which repaint already does (indirectly). I will posit that regardless you are far better off using Swing and its lightweight components, that there is a better way of solving whatever underlying problem you are having that makes you feel impelled to override update().

My paint() function handles redraws invoked by the system.
Update() does my repaint() calls.
In update() I only draw a counter, in paint() the whole screen().

It is for vanheusden.com/java/CoffeeSaint/

[camickr]

It appears you don't understand how painting works. Remember, your original question was about JFrame, which indicates you are attempting to create a Swing application.

In Swing custom painting is done by overriding the paintComponent() method of a component like JPanel.

When using AWT custom painting was done by overriding paint() and update(). I find people generally use this approach because they found some 10 year old code lying around.

People generally use Swing over AWT because it is far more flexible, more current and advanced than AWT.