拖动画图程序

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

public class Main extends JFrame implements MouseMotionListener, MouseListener {
    static Main frm = new Main();
    int px1,py1,px2,py2,status = 0;
    int rpx1,rpx2,rpy1,rpy2;

    @Override
    public void mouseClicked(MouseEvent e) {

    }

    @Override
    public void mousePressed(MouseEvent e) {

    }

    @Override
    public void mouseEntered(MouseEvent e) {

    }

    @Override
    public void mouseExited(MouseEvent e) {

    }

    @Override
    public void mouseDragged(MouseEvent e) {
        Graphics g = this.getGraphics();
        g.setColor(Color.yellow);
        g.setXORMode(Color.black);
        if(status == 1) {
            g.drawOval(px1,py1,px2,py2);
        } else {
            px1 = e.getX();
            px2 = e.getY();
            status = 1;
        }
        px2 = Math.abs(e.getX()-px1);
        py2 = Math.abs(e.getY()-py1);
        g.drawOval(px1,py1,px2,py2);
        rpx1 = px1; rpy1 = py1; rpx2 = px2; rpy2 = py2;
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        px1 = e.getX();
        py1 = e.getY();
        status = 0;
    }

    @Override
    public void mouseReleased(MouseEvent e) {
        Graphics g = this.getGraphics();
        g.setColor(Color.red);
        g.drawOval(rpx1,rpy1,rpx2,rpy2);
    }

    public static void main(String[] args) {
        frm.setTitle("Oval");
        frm.setSize(750,690);
        frm.addMouseMotionListener(frm);
        frm.addMouseListener(frm);
        frm.setVisible(true);
        frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}