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wtd

Sat Nov 25, 2006 5:46 pm


[Tip] Implementing Listeners

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Ok, I'm getting annoyed enough at seeing this that I can't help but post something about it.

When you have distinct controls in your app, please, for the love of everything sacred, do not have your container implement ActionListener.

What do I mean by this?

Well, avoid a situation like:

class Window extends JFrame implements ActionListener {
   private JButton greetButton;
   private JTextField nameEntryTextField;

   // ...

   public void actionPerformed(ActionEvent e) {
      if (e.getSource() == greetButton) {
         String inputName = NameEntryTextField.getText();

         if (!inputName.equals("")) {
            System.out.println("Hello, " + inputName + "!");
         }
      }
   }
}

Instead, use anonymous inner classes to clear this up.

class Window extends JFrame {
   private JButton greetButton;
   private JTextField nameEntryTextField;

   public Window() {
      // setup stuff...

      greetButton = new JButton("Greet!");
      greetButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            String inputName = nameEntryTextField.getText();

            if (!inputName.equals("")) {
               System.out.println("Hello, " + inputName + "!");
            }
         }
      });
   }
}


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Regeane

Mon Dec 04, 2006 1:13 pm



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please excuse if this is ignorance, but what is the benefit to the inner class rather than implementing?


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wtd

Mon Dec 04, 2006 1:18 pm



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Imagine you have ten things that respond to actions in your GUI.  Now, ask yourself if you want to have a ten-way conditional branch.  :)


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Regeane

Mon Dec 04, 2006 2:11 pm



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what if you only had one condition? is it still better to do it that way, or does it really matter?


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Aziz

Fri Dec 08, 2006 8:51 am



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Just remember, there's sometimes problems accessing things from inside an inner class. for example, 'this' would refer to the anonymous class, NOT the main class. Also, I've run into errors saying a member has to be declared final, or some such. I usually call a method from inside this if it's a big deal, (such as importing files). Something simple (like disabling a button) usually resides in the inner class, for me.