Question

In the GUI book we use in class there are many examples of how graphical user interfaces are made in Java. So many examples, that I’m very confused regarding which one should be used when it comes down to a big application.

So I’ve seen examples

• in which the main class extends JFrame
• where the JFrame object is created inside the main method
• where the main class extends JFrame AND implements ActionEvent interface
• where Listener classes are declared inside the main class

Sure, I can work with all of these, but right now, as I don’t have any kind of experience, I don’t see the benefit of using any of them. Is actually one of them the correct way to do it or it depends on my sittuation?

Thank you!

Answer 1

"Is A" or "Has A"? This is the question that should be asked when considering extending a class. If the new class "Is A" frame, extend frame, but if the class just needs a reference to a frame, don’t extend.

In fact, if a custom component is required, extend a JComponent or JPanel, then add that to a frame, ..applet, window, JInternalFrame, dialog, constraint of a layout, part of a split pane..

Listeners

As to the listeners. Rather than traverse a huge if/else structure in the single actionPerformed() method to determine the required action, it is more optimal to either:

1. Create a listener for each control that needs it.
2. Create an instance of an AbstractAction that might be used for multiple controls (‘copy’ button, menu item etc.).

Summary

So (generally) for the:

1. JFrame, don’t extend.
2. Listeners, create and add as needed.