Add a listener inside or outside get method

Question

I'm learning Swing and have composed an interface using a series of get methods to add components. Is it a good practise to add a Listener inside a get method as follows? I'd like to make things as decoupled as possible.

 private JButton getConnectButton() {
  if (connectButton == null) {
   connectButton = new JButton();
   connectButton.setText("Connect");
   connectButton.setSize(new Dimension(81, 16));
   connectButton.setLocation(new Point(410, 5));

   connectButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
     // actionPerformed code goes here
    }
   });

  }
  return connectButton;
 }

Answer 1

It seems like you're implementing some lazy initialization of the connectButton. That's probably fine, although, I would do it like this:

private void createButton() {
    connectButton = new JButton(new AbstractAction("Connect") {
        public void actionPerformed(ActionEvent e) {
            // actionPerformed code goes here
        }
    });
    connectButton.setText("Connect");

    // Rely on some LayoutManager!
    //connectButton.setSize(new Dimension(81, 16));
    //connectButton.setLocation(new Point(410, 5));
}

private synchronized JButton getConnectButton() {
    if (connectButton == null)
        createButton();

    return connectButton;
}

Note the use of synchronized. It ensures that the following scenario won't happen:

• Thread 1 calls getConnectButton() and sees connectButton == null
• Thread 2 calls getConnectButton() and sees connectButton == null
• Thread 1 calls createButton
• Thread 2 calls createButton.

There are probably nicer ways to synchronize the button-construction, but this is one way.

Answer 2

From my extensive practice as a Swing developer I can tell you that it's not good practice to obtain component instances in this manner(via getters). I generally setup the UI for a Frame/Dialog in some method like initComponents() and afterwards add all the listeners in some method like addListeners(). I'm not sure if that there is a single best practice as how to do things - there a lot of options and personal preferences. Generally, however, lazy init of components that you'll need anyways(like this button I presume) is unneeded.

Also - you should really consider using some layout manager such a MiG and avoid hardcoded component sizes.