사각형 크기 줄였다 컸다하는거

package ex;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.*;

import javax.swing.JFrame;
import javax.swing.JPanel;

class MyPanel1234 extends JPanel implements Runnable{
 Color color;
 int x=0,y=0,sx=5,sy=5;
 
 public MyPanel1234(){
         new Thread(this).start();
 }
 
 

 
 
 
 public void paintComponent(Graphics g)
 {
  super.paintComponent(g);;
  g.setColor(Color.RED);
  if(x < -300 || x> 0){ sx=-sx;}
  if(y < -300 || y>0) sy=-sy;
  System.out.println("x: "+x+"sx: "+sx);
  g.fillRect(500,500,x=x-sx,y=x-sy);

 }

 

 public void run() {
  while(true){
   try {
    Thread.sleep(20);
   
   } catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }this.repaint();
  }
 
 }

}

public class RectTest1 extends JFrame{
 public RectTest1(){
  this.setTitle("zz");
  this.setSize(700,700);
  this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
  MyPanel1234 mp = new MyPanel1234();
 
  add(mp);
  this.setVisible(true);
 }
 
 public static void main(String[] args)
 {
  new RectTest1();
 }
}