Java Simple ActionListener Questions

Question

I have a main class in a program that launches another class that handles all the GUI stuff. In the GUI, i have a button that i need to attach an ActionListener to.

The only problem is, the code to be executed needs to reside within the main class.

How can i get the ActionPerformed() method to execute in the main class when a button is clicked elsewhere?

Answer 1

Implement ActionListener in your main class and add the main class instance as a listener on your GUI button.

Answer 2

Make your controller ("main" class) implement the ActionListener interface, then pass a reference to the view class:

public class View extends JFrame {
  public View(final ActionListener listener) {
   JButton button = new JButton("click me");
   button.addActionListener(listener);
   button.setActionCommand("do_stuff");

   getContentPane().add(button);

   pack();
   setVisible(true);
  }
 }

 public class Control implements ActionListener {

  public Control() {
   new View(this);
  }

  @Override
  public void actionPerformed(ActionEvent e) {
   if (e.getActionCommand().equals("do_stuff")) {
    // respond to button click
   }
  }
 }

It can also be done with Actions, but that's more useful where you want one piece of code to respond to many buttons.

Answer 3

Implement an anonymous inner class as ActionListener on the button, then call the method on your main class. This creates less dependencies and avoids the tag & switch style programming that implementing the ActionListener interface on a main class tends to promote.

In either case it will create a cycle in your dependency graph: the main class will know about the button and the button will need to call the main class. This might not be a good idea since it will make it hard to compose things in any other way. But without further information it is hard to judge the situation or recommend anything concrete.