Graphical User Interfaces - Building Java Programs: A Back to Basics Approach - page 867

Now that our ActionListener code is complete, we have to create and start the
timer that invokes the listener. Let's add code for the timer to the constructor for the
AnimatedRectPanel :
// set up timer to animate rectangles every 100 ms
Timer time = new Timer(100, this);
time.start();
Here's the complete second version of the AnimatedRectPanel program that
incorporates all of these features:
1 // A panel that draws animated rectangles on its surface.
2
3 import java.awt.*;
4 import java.awt.event.*;
5 import javax.swing.*;
6
7 public class AnimatedRectPanel2 extends JPanel
8 implements ActionListener {
9 private Point p1; // location of first rectangle
10 private Point p2; // location of second rectangle
11 private int dx; // amount by which to move horizontally
12 private int dy; // amount by which to move vertically
13
14 public AnimatedRectPanel2() {
15 p1 = new Point(20, 40);
16 p2 = new Point(60, 10);
17 dx = 5;
18 dy = 5;
19
20 // set up timer to animate rectangles every 100 ms
21 Timer time = new Timer(100, this );
22 time.start();
23 }
24
25 // draws two rectangles on this panel on the screen
26 public void paintComponent(Graphics g) {
27 super .paintComponent(g); // call JPanel's version
28 g.setColor(Color.RED);
29 g.fillRect(p1.x, p1.y, 70, 30);
30 g.setColor(Color.BLUE);
31 g.fillRect(p2.x, p2.y, 20, 80);
32 }