Multiple Frames and Windows - strange paint behaviour

Question

Hi,
I came across this one today, and was wondering if anyone had seen this behaviour before. Here is the simplest code I can make it happen with...
public class StrangenessTest {
public static void main(String []args) {
JFrame f1 = new JFrame("f1");
JFrame f2 = new JFrame("f2");
JPanel pOne = new JPanel() {
public void paintComponent(Graphics g) {
g.fillRect(100, 100, 20, 20);
JPanel pTwo = new JPanel() {
public void paintComponent(Graphics g) {
g.drawLine(100, 100, 150, 150);
f1.getContentPane().add(pOne);
f2.getContentPane().add(pTwo);
pOne.setBounds(0, 0, 200, 200);
pTwo.setBounds(0, 0, 200, 200);
f1.setBounds(100, 100, 200, 200);
f2.setBounds(300, 100, 200, 200);
f1.setVisible(true);
f2.setVisible(true);
Basically, everything that gets painted in JPanel pOne ends up in pTwo as well. That is, if you run the code below (on JDK 1.3.1_01 or 1.4.1_02), you get two frames, the first one has a square in it, the second one has a square and a line.
If you reverse the order of the setVisible's at the end of the main(), you reverse the symptoms - i.e. the first frame ans a square and a line, the second frame has a line.
Am I missing something in the docos, or is this a bug?
(btw, the strangeness goes away if I add a super.paintComponent() into the JPanel that is drawn last).
Comments? Suggestions?
Cheers,
Joe

Answer 1

Of course, adding a setOpaque(false) to the constructor of the panel fixes the problem!
Sorry about that.
Cheers,
Joe