how to unpaint my circle

[vettera]

i animated a circle that goes down the page and when it goes down. It does not erase the previous circle. I was wondering if there was a certain function for it.
Code:

import javax.swing.*;
import java.awt.*;
import java.awt.geom.Ellipse2D;
public class ball extends JFrame implements Runnable {
	int y = 0;
	final int Delay = 5;
	Thread anima;
	
    public ball(){
    super("Moving Ball");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(500,500);
    setVisible(true);
    setResizable(false);
    setBackground(Color.white);
    }
    public void addNotify(){
    	super.addNotify();
    	anima = new Thread(this);
    	anima.start();
    }
	public void paint(Graphics g){
		Graphics2D ga = (Graphics2D)g;   
		Ellipse2D e = new Ellipse2D.Float(200,y,100,100);
		ga.setColor(new Color(75,0,130));
		ga.fill(e);
	    ga.draw(e);
	}
    public void cycle(){
    	y++;
    	if(y >= 500){
    		y = 0;
    	}
    }
    public void run(){
    	long starttime , total , sleep;
    	starttime = System.currentTimeMillis();
    	while(true){
    		cycle();
    		repaint();
    		total = System.currentTimeMillis() - starttime;
    		sleep = Delay - total;
    		if(sleep < 0){
    			sleep = 2;
    		}
    		try {
				Thread.sleep(sleep);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			starttime = System.currentTimeMillis();
    	}
    }
    public static void main(String[] args ){
    	ball b = new ball();
    }
}

[Fubarable]

Your primary problem is that your paint method doesn't call the super.paint(g); method as its first method call. But you have other problems as well:

• You shouldn't be drawing directly in a JFrame and
• You especially shouldn't be animating in a JFrame, unless you want choppy animations.
• Instead draw/animate in a JPanel
• and do your drawing in its paintComponent method override, not its paint method.
• The first line of your paintComponent method override should be a call to the super's paintComponent method (analogous to for the paint method).
• Rather than use background threads for simple animations, consider using a Swing Timer.

Also, please check out my link on using code tags when posting code here.

Much luck!

[DarrylBurke]

• To improve efficiency, don't construct a new Ellipse2D every time through the painting method. Maintain one Ellipse2D as an instance field, possibly final, and mutate it before painting.
• Similarly, cache the Color(75,0,130), possibly as a static final field.

db