Question

I have a view that has several “flag” buttons (JToggleButton). When the user clicks a flag button, I want to update an array that keeps track of which buttons are flagged. This is pretty simple, and here is what I have done:

...
   bflag[i].addItemListener(this); //View listens to state change
...

void itemStateChange(ItemEvent ie) {
   try {
      jtb = (JToggleButton)ie.getSource();
      //Update mark array
   }
   catch (ClassCastException cce) {}
}

This works just fine, but it is ugly with the try/catch. I would much prefer to do something like this:

void itemStateChange(ItemEvent ie) {
   handleStateChange(ie.getSource());
}

void handleStateChange(JToggleButton jtb) {
   //handle state change
}

void handleStateChange(Object o) {}

This is much nicer, but the only problem is that the Object method will fire even if the source is a JToggleButton (because a JToggleButton is an Object after all).

I have also considered using double dispatch, but this would require overriding the JToggleButton method that fires itemStateChange(), and I don’t know what that is (and that seems unsafe).

Any suggestions on how to get this to work without a try/catch, conditional check, etc.?

Answer 1

You will have to check for the Type explicitly I think.

  if(ie.getSource() instanceof JToggleButton){
      //toggle button logic
  }else{
      //something else
  }

Alternatively you can use anonymous inner classes to implement your listeners and avoid having to check the source altogether.

---

Something like this:

 toggleBtn.addItemListener(new ItemListener(){
         public void itemStateChange(ItemEvent ie){
            //handle toggle button event
         }
 });