Question

This may have been asked many times before or I don’t know what to search for to get an answer. What I have got is a JFrame that loads in several JPanels. What I am having difficulty in is updating the contents of one JPanel from another. So say I have the following:

JFrame1.JPanel1.JButtonA
JFrame1.JPanel2.JButtonB

When JButtonA is pressed I want JButtonB to have its text changed. Of course this isn’t what I want to do but is a simple example of what I would like to achieve. Where am I going wrong? How to get a reference to an object without making everything a singleton?

Answer 1

The easiest way is of course to remember a reference to JFrame1 when construction JPanel1:

JPanel1 p1 = new JPanel1(this);

and remember and use that in JPanel1:

public JPanel1(JFrame1 f1) {
    this.f1 = f1;
}
...
public void actionPerformend(...) {
    f1.getPanel2().getButtonB().setText("A is pressed");
}

But that’s bad.

Instead, think about what clicking A really means (for example pauze game). Then create a PauzeGameEventListener interface, implemented by JPanel2 (for example the chessboard) and make JPanel1 (for example the game controls panel) fire a PauzeGameEvent to all listeners. That way, when your JPanel3 (for example score panel) or non-gui stuff (for example the AI player) needs to be aware of that too, you’re not littering the JPanel1 code.