如何使用JFrame完成动态模拟时钟

import javax.swing.*;import java.awt.*;import java.util.*;import java.lang.Thread;import java.text.DecimalFormat; public class StillClock extends JPanel {   /**   * @param args   */  private int hour;  private int minute;  private int second;     //构造函数  public StillClock() {    setCurrentTime();  }   //返回小时  public int getHour() {    return hour;  }        public int getMinute() {    return minute;  }           public int getSecond() {    return second;  }        //绘制时钟  protected void paintComponent(Graphics g) {         super.paintComponent(g);    //初始化    int clockRadius = (int)(Math.min(getWidth(), getHeight()) * 0.8 * 0.5);    int xCenter = getWidth() / 2;    int yCenter = getHeight() / 2;    //画圆    g.setColor(Color.black);    g.drawOval(xCenter - clockRadius, yCenter - clockRadius, 2 * clockRadius, 2 * clockRadius);    g.drawString("12", xCenter - 5, yCenter - clockRadius + 15);    g.drawString("9", xCenter - clockRadius + 3, yCenter + 5);    g.drawString("3", xCenter + clockRadius - 10, yCenter + 3);    g.drawString("6", xCenter - 3, yCenter + clockRadius - 3);    //画秒针    int sLength = (int)(clockRadius * 0.8);    int xSecond = (int)(xCenter + sLength * Math.sin(second * (2 * Math.PI / 60)));    int ySecond = (int)(yCenter - sLength * Math.cos(second * (2 * Math.PI / 60)));         g.setColor(Color.red);    g.drawLine(xCenter, yCenter, xSecond, ySecond);         //画分针    int mLenth = (int)(clockRadius * 0.65);    int xMinute = (int)(xCenter + mLenth * Math.sin(minute * (2 * Math.PI / 60)));    int yMinute = (int)(xCenter - mLenth * Math.cos(minute * (2 * Math.PI / 60)));    g.setColor(Color.blue);    g.drawLine(xCenter, yCenter, xMinute, yMinute);         //画时针    int hLength = (int)(clockRadius * 0.5);    int xHour = (int)(xCenter + hLength * Math.sin((hour % 12 + minute / 60.0) * (2 * Math.PI / 12)));    int yHour = (int)(yCenter - hLength * Math.cos((hour % 12 + minute / 60.0) * (2 * Math.PI / 12)));    g.setColor(Color.green);    g.drawLine(xCenter, yCenter, xHour, yHour);         //画数字时钟    g.setColor(Color.black);    DecimalFormat s=new DecimalFormat("00");    g.drawString(s.format(getHour()) + ":" + s.format(getMinute()) + ":" + s.format(getSecond()), xCenter - 22, yCenter - clockRadius - 15);       }     public void setCurrentTime() {    Calendar calendar = new GregorianCalendar();         this.hour = calendar.get(Calendar.HOUR_OF_DAY);    this.minute = calendar.get(Calendar.MINUTE);    this.second = calendar.get(Calendar.SECOND);  }        public static void main(String[] args) {    // TODO Auto-generated method stub    JFrame frame = new JFrame("DiaplayClock");        frame.setResizable(false);    frame.setTitle("DiaplayClock");    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    frame.setSize(300,350);    frame.setVisible(true);         while(true) {      StillClock clock = new StillClock();      frame.getContentPane().add(clock);      clock.setVisible(true);      frame.validate();      try {        Thread.sleep(1000);               }      catch (InterruptedException e) {        e.printStackTrace();       }      clock.setVisible(false);      frame.remove(clock);      clock = null;      frame.validate();           }   }}