Separating GUI from logic in Java

Question

I went through plenty of articles and (imo too complex) examples of how to separate GUI from the rest of the program logic in Java, and to be completely honest, I still have no clue.

Could someone give me a hint of how to do it on this simple example, with just one button?

Let's say there is a button in the Window class:

JButton firstButton = new JButton("My first button");      
btnCreateProject.setBounds(100, 100, 80, 30);
frame.getContentPane().add(firstButton);

and let's say this button would call a constructor of the Employee class. So, I could do it like this:

JButton firstButton = new JButton("My first button");
firstButton.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e) {
      .....constructor calling, and rest of the code....
   }
});
btnCreateProject.setBounds(100, 100, 80, 30);
frame.getContentPane().add(firstButton);

But this is exactly what I DO NOT want. I want my Window class to be just pure GUI, with buttons, radio boxes, and other stuff, with it's properties. Nothing more. I would like to have all the listeners in another class, let's say Controller, and from this class I would call all the needed methods.

Could someone give me an example of how to do it with this simple button? Thank you very much.

Answer 1

You are drawing a distinction of degree, not kind. Your GUI code cannot be completely separated from program logic, else it would be a static work of modern art.

The various kinds of AWT/Swing listener classes do separate GUI from logic, into altogether separate classes. You do not, however, need to implement listeners as anonymous inner classes; perhaps it would feel better to you to implement them as ordinary, top-level classes instead. Alternatively, you might find that it suits you to model program behaviors via classes implementing the Action interface. Then you can assign those behaviors to controls (buttons, menu items) via the controls' setAction() method.

Any way around, however, the code that sets up your GUI has to somehow know about both the GUI components and the logic that needs to be hooked up to them, else there's no way it could do its job.