Question

OK, so if I add an ActionListener to a GUI element, and it’s the only element I use that ActionListener with, does it matter which of the following lines (a,b) I use to get the checkbox selected state?

final JCheckBox checkbox = (JCheckBox)this.buildResult.get("cbDebugTick");
checkbox.addActionListener(new ActionListener() {
    @Override public void actionPerformed(ActionEvent event){               
            boolean bChecked =
            // (a) checkbox.isSelected();
            // (b) ((JCheckBox)event.getSource()).isSelected();
            model.setPrintDebugOn(bChecked);
        }
});

It makes sense to me that if I add the ActionListener object to multiple GUI elements, then I should use (b).

And in (b), is it OK to blindly cast event.getSource() to JCheckBox, since I’m the one who added the action listener, or should I program defensively and do an instanceof check?

note: this question is in the context of event listeners in general; kdgregory has some good points below specifically re: checkboxes which I had neglected to consider.

Answer 1

in (b) to be rigourous, you should indeed do a instanceof check, but it’s not that important. I would think both these lines are fine and acceptable, though (b) would be “better code”

Although, what is usually done in an action listener is simply call another method customized to your checkbox. So it would look like something like this:

 @Override public void actionPerformed(ActionEvent event) {                                  
    //your treatment would be in this method, where it would be acceptable to use (a)                  
    onCheckBoxActionPerformed(event)
}