一个简单的Timer动画，就是没显示，求指点啊

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics;
public class MovingCar extends JFrame
{
public MovingCar(String s)
{
super(s);
CarPanel MyCar=new CarPanel();
add(MyCar);
}
public static void main(String [] args)
{
JFrame mine=new MovingCar("my window");
mine.setSize(500,300);
mine.setLocation(200,200);
mine.setVisible(true);
}
public class CarPanel extends JPanel
{
public CarPanel()
{
Timer timer=new Timer(1000,new TimeActionListener());
timer.start();
}
}
class TimeActionListener implements ActionListener
{
public void actionPerformed(ActionEvent g)
{
repaint();
}
}
protected void paintComponent(Graphics g)
{
super.paintComponents(g);
int px=0;
int py=5;
if(px>=getWidth())
px=0;
px+=5;
g.drawString("mmmm",px,py);
}
}

[code="java"]
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class MovingCar extends JFrame {
public MovingCar(String s) {
super(s);
CarPanel MyCar = new CarPanel();
add(MyCar);
}

public static void main(String[] args) {
    JFrame mine = new MovingCar("my window");
    mine.setSize(500, 300);
    mine.setLocation(200, 200);
    mine.setVisible(true);
    mine.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public class CarPanel extends JPanel {
    int px=0;
    public CarPanel() {
        Timer timer = new Timer(200, new TimeActionListener());
        timer.start();
    }

    class TimeActionListener implements ActionListener {
        public void actionPerformed(ActionEvent g) {
            repaint();
        }
    }

    protected void paintComponent(Graphics g) {
        super.paintComponents(g);

        g.clearRect(0, 0, getWidth(), getHeight());

        int py = 50;
        if (px >= getWidth())
            px = 0;
        px += 5;
        g.setColor(Color.red);
        g.drawString("mmmm", px, py);
    }
}

}
[/code]

刚才发错了，我改了一下，可以了

[code="java"]import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics;
public class MovingCar extends JFrame
{
public MovingCar(String s)
{
super(s);
CarPanel MyCar=new CarPanel();
add(MyCar);
}
public static void main(String [] args)
{
JFrame mine=new MovingCar("my window");
mine.setSize(500,300);
mine.setLocation(200,200);
mine.setVisible(true);
}
public class CarPanel extends JPanel
{
public CarPanel()
{
Timer timer=new Timer(1000,new TimeActionListener());
timer.start();
}
}
class TimeActionListener implements ActionListener
{
public void actionPerformed(ActionEvent g)
{
repaint();
}
}
protected void paintComponent(Graphics g)
{
super.paintComponents(g);
int px=0;
int py=5;
if(px>=getWidth())
px=0;
px+=5;
g.drawString("mmmm",px,py);
}
} [/code]