一、核心的表达式

因为需要动态显示小时的指针、分钟的指针、秒的指针的位置，所以确认三个指针的角度非常重要； 

X：三个指针相交的原点的X坐标；

Y：三个指针相交的原点的Y坐标；

HOUR_LENGTH、MINUTE_LENGTH、SECOND_LENGTH表示时针、分针、秒针的长度；

hour、minute、second表示现在是几时、几分、几秒；  

hourLine.x2 = X+HOUR_LENGTH*Math.cos(hour*(Math.PI/6)-Math.PI/2);
hourLine.y2 = Y+HOUR_LENGTH*Math.sin(hour*(Math.PI/6)-Math.PI/2);
minLine.x2 = X+MINUTE_LENGTH*Math.cos(minute*(Math.PI/30)-Math.PI/2);
minLine.y2 = Y+MINUTE_LENGTH*Math.sin(minute*(Math.PI/30)-Math.PI/2);
secondLine.x2 = X+SECOND_LENGTH*Math.cos(second*(Math.PI/30)-Math.PI/2);
secondLine.y2 = Y+SECOND_LENGTH*Math.sin(second*(Math.PI/30)-Math.PI/2);

二、怎样动态显示

简单的说就是每一秒更新一次屏幕，因此用Timer和TimerTask非常符合要求；每一秒刷新一次；

三、代码

package org.Demo00;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.geom.Ellipse2D;import java.awt.geom.Line2D;import java.util.Calendar;import java.util.GregorianCalendar;import java.util.Timer;import java.util.TimerTask;import javax.swing.JFrame;import javax.swing.JPanel;public class Test5 extends JFrame { MyPanel clockPanel; Ellipse2D.Double e; int x; int y; Line2D.Double hourLine; Line2D.Double minLine; Line2D.Double secondLine; GregorianCalendar calendar; int hour; int minute; int second; public static final int X = 60; public static final int Y = 60; public static final int X_BEGIN = 10; public static final int Y_BEGIN = 10; public static final int RADIAN = 50; public Test5() {  setSize(300, 400);  clockPanel = new MyPanel();  add(clockPanel);  Timer t = new Timer();  Task task = new Task();  t.schedule(task, 0, 1000); } public static void main(String[] args) {  Test5 t = new Test5();  t.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  t.setVisible(true); } class MyPanel extends JPanel {  public MyPanel() {   e = new Ellipse2D.Double(X_BEGIN, Y_BEGIN, 100, 100);   hourLine = new Line2D.Double(X, Y, X, Y);   minLine = new Line2D.Double(X, Y, X, Y);   secondLine = new Line2D.Double(X, Y, X, Y);  }  public void paintComponent(Graphics g) {   super.paintComponent(g);   Graphics2D g2 = (Graphics2D) g;   g2.drawString("12", 55, 25);   g2.drawString("6", 55, 105);   g2.drawString("9", 15, 65);   g2.drawString("3", 100, 65);   g2.draw(e);   g2.draw(hourLine);   g2.draw(minLine);   g2.draw(secondLine);  } } class Task extends TimerTask {  public void run() {   calendar = new GregorianCalendar();   hour = calendar.get(Calendar.HOUR);   minute = calendar.get(Calendar.MINUTE);   second = calendar.get(Calendar.SECOND);   hourLine.x2 = X + 40 * Math.cos(hour * (Math.PI / 6) - Math.PI / 2);   hourLine.y2 = Y + 40 * Math.sin(hour * (Math.PI / 6) - Math.PI / 2);   minLine.x2 = X + 45     * Math.cos(minute * (Math.PI / 30) - Math.PI / 2);   minLine.y2 = Y + 45     * Math.sin(minute * (Math.PI / 30) - Math.PI / 2);   secondLine.x2 = X + 50     * Math.cos(second * (Math.PI / 30) - Math.PI / 2);   secondLine.y2 = Y + 50     * Math.sin(second * (Math.PI / 30) - Math.PI / 2);   repaint();  } }}