Swing中依据鼠标拖拽来画出矩形的实现方法

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
 class Rect extends JFrame{
  public static void main(String[] args) {
    Rect r=new Rect();
  }
  Draw draw=new Draw();
  public Rect()
  {
    this.add(draw);
    this.addMouseListener(draw);
    this.setSize(500,500);
    this.setLocation(400,400);
    this.setVisible(true);
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
}
class Draw extends JPanel implements MouseListener {
  int x1 = 0;
  int y1 = 0;
  int x2 = 0;
  int y2 = 0;

  public void paint(Graphics g) {
//    super.paint(g);
    g.setColor(Color.BLUE);
    g.drawRect(x1, y1, x2 - x1, y2 - y1);

  }

  @Override
  public void mouseClicked(MouseEvent e) {

  }

  @Override
  public void mousePressed(MouseEvent e) {
    x1 = e.getX();
    y1 = e.getY();
  }

  @Override
  public void mouseReleased(MouseEvent e) {
    x2 = e.getX();
    y2 = e.getY();
    this.repaint();
  }

  @Override
  public void mouseEntered(MouseEvent e) {

  }

  @Override
  public void mouseExited(MouseEvent e) {
  }
}