Question

Say, you have a subclass of JFrame, and use it to create your own custom JFrame. In this class (we’ll call it mainFrame), we create a reference to another custom JFrame class (we’ll call this one sidePanel).

In sidePanel, you have different buttons, radio buttons,..

My question is, is there a way to notify mainFrame the user presses on a button?

I’ve created a (untested) example of what I mean:

class mainFrame extends JFrame {
   public mainFrame() {
      super("main frame");
      //...........
      sidePanel panel = new sidePanel();
      //...........
   }
   public static void main(String[] args) {
      mainFrame mainF = new mainFrame();
      //.........
   }
}

And the sidePanel class:

class sidePanel extends JFrame {

   public sidePanel() {
      super("sidePanel frame");
      //...........
      JButton button1 = new JButton();
      button1.addActionListener(new ActionListener() {  
          public void actionPerformed(ActionEvent e)
            {
               //Notify mainFrame somehow button is pressed
          }});
      //...........
    }
}

Answer 1

To notify mainFrame of an event, the SidePanel instance (really bad name for a Frame) must have a reference to mainFrame. Pass mainFrame as an argument of the SidePanel constructor, and callback mainFrame from the actionPerformed method in SidePanel:

SidePanel panel = new SidePanel(this);

and in SidePanel:

public void actionPerformed(ActionEvent e) {
    mainFrame.buttonHasBeenClicked();
    ...
}

This tightly couples both classes though. A way to decouple them is to make the SidePanel object accept listeners for custom events, and to fire such an event when the button is clicked. The mainFrame would construct the SidePanel instance, and add itself (or an inner anonymous class instance) as a listener to the sidePanel.

See this page for an example.