J2SE Canvas应用：设计一个计时器部件

Canvas类：

 1:  import java.awt.Frame;

 2:  import java.awt.event.WindowAdapter;

 3:  import java.awt.event.WindowEvent;

 4:  

 5:  import java.awt.AWTEvent;

 6:  import java.awt.Canvas;

 7:  import java.awt.Color;

 8:  import java.awt.Graphics;

 9:  import java.awt.event.MouseEvent;

10:  import java.text.ParseException;

11:  import java.text.SimpleDateFormat;

12:  import java.util.Date;

13:  

14:  class StopWatch extends Canvas implements Runnable {

15:      private long startTime = 0;

16:      private long endTime = 0;

17:      private boolean bStart = false;

18:  

19:      public StopWatch() {

20:          enableEvents(AWTEvent.MOUSE_EVENT_MASK);

21:          setSize(80, 30);

22:      }

23:  

24:      protected void processMouseEvent(MouseEvent e) {

25:          if (e.getID() == MouseEvent.MOUSE_PRESSED) {

26:              bStart = true;

27:              startTime = endTime = System.currentTimeMillis();

28:              repaint();

29:              new Thread(this).start();

30:          } else if (e.getID() == MouseEvent.MOUSE_RELEASED) {

31:              bStart = false;

32:              repaint();

33:          }

34:      }

35:  

36:      @Override

37:      public void paint(Graphics g) {

38:          super.paint(g);

39:          // 时间值的小时，分，秒用两位数字显示，不足两位的部分前面加0，即 "HH:mm:ss"

40:          SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");

41:          Date elapsedTime = null;

42:          try {

43:              elapsedTime = sdf.parse("00:00:00");

44:          } catch (ParseException e) {

45:              e.printStackTrace();

46:          }

47:          // elapsedTime.setTime(endTime - startTime)不是"00:00:00" 而是"08:00:00"

48:          elapsedTime.setTime(endTime - startTime + elapsedTime.getTime());

49:          String display = sdf.format(elapsedTime);

50:          g.drawRect(0, 0, 78, 28);

51:          g.fill3DRect(2, 2, 75, 25, true);

52:          g.setColor(Color.red);

53:          g.drawString(display, 10, 20);

54:      }

55:  

56:      @Override

57:      public void run() {

58:          while (bStart) {

59:              try {

60:                  Thread.sleep(500);

61:              } catch (InterruptedException e) {

62:                  e.printStackTrace();

63:              }

64:              endTime = System.currentTimeMillis();

65:              repaint();

66:          }

67:      }

68:  

69:  }

Main类（程序入口）：

 1:  public class TestStopWatch {

 2:      public static void main(String[] args) {

 3:          Frame f = new Frame("StopWatch");

 4:          f.add(new StopWatch());

 5:          f.setSize(200, 200);

 6:          f.setVisible(true);

 7:          f.addWindowListener(new WindowAdapter() {

 8:  

 9:              @Override

10:              public void windowClosing(WindowEvent e) {

11:                  super.windowClosing(e);

12:                  System.exit(0);

13:              }

14:          });

15:      }

16:  }