Graphical User Interfaces - Building Java Programs: A Back to Basics Approach - page 868

33
34 // called at regular intervals by timer to redraw the panel
35 public void actionPerformed(ActionEvent event) {
36 p1.x += dx;
37 p2.y += dy;
38 if (p1.x <= 0 || p1.x + 70 >= getWidth()) {
39 dx = -dx; // rectangle 1 has hit left/right edge
40 }
41 if (p2.y <= 0 || p2.y + 80 >= getHeight()) {
42 dy = -dy; // rectangle 2 has hit top/bottom edge
43 }
44
45 repaint(); // instruct the panel to redraw itself
46 }
47 }

Here's the graphical window that is produced as output, which animates the rec-
tangles as we intended:

Table 14.10 lists several methods of the Timer class.

Table 14.10 Useful Methods of Timer Objects

public Timer(int msDelay, ActionListener listener)
Creates a Timer that activates the given ActionListener every msDelay milliseconds.
public void start()
Tells the timer to start ticking and to activate its ActionListener .
public void stop()
Tells the timer to stop ticking and not to activate its ActionListener .