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From: Jail Bush Cronies <do.not@ask.me>
Newsgroups: comp.lang.java.programmer
Subject: Re: I need a different approach - suggestions please
Date: Wed, 27 Jun 2012 18:46:59 -0400
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On 27/06/2012 6:21 PM, Patricia Shanahan wrote:
> On 6/27/2012 2:44 PM, bilsch wrote:
> ...
>> The listeners all call a statement in the second file:
>>
>> public void actionPerformed(ActionEvent event)
>>
>> so I don't understand how a button listener can be different from
>> another button listener.
>
> You can write several different implementing classes for an interface
> such as ActionListener. You can then create different instances of the
> same implementing class.
>
> For example, you could have a NumberKeyListener class that implements
> ActionListener, and takes a constructor parameter that tells it the
> value associated with its button. On the other hand, I would have a
> different class for dealing with backspace.
>
> Code like:
>
> one.addActionListener(new NumberKeyListener(1));
> two.addActionListener(new NumberKeyListener(2));
>
> would get rid of a lot of checking which button was pressed.

Another option uses the ActionEvent the listener gets passed, a 
parameter that's frequently ignored:

public void actionPerformed (ActionEvent e) {
     JButton btn = (JButton)(e.getSource());
     String btnTxt = btn.getText();
     // btnTxt should be "0", "1", ..., or "9".
     // Do something with it.
}

Of course, this action listener will blow up if used on something other 
than a JButton. You also might not like the results if you later 
localize the button labels using a ResourceBundle or something. :) In 
the event that that sort of thing is likely, the numeric-parameter 
approach Patricia suggested is more robust. Another possibility is:

private static Map<JButton,Integer> buttonMap;

...

for (int i = 0; i < 10; i++) {
     JButton btn = new JButton("" + i);
     btn.addActionListener(new NumberKeyListener());
     buttonMap.add(btn,i);
}

...

public void actionPerformed (ActionEvent e) {
     int btnNum = buttonMap.get(e.getSource());
}

Note: will throw NPE if attached to something other than a button that's 
in buttonMap. Also, for buttonMap to be visible in actionPerformed, 
NumberKeyListener needs to be a nested class of the class with the rest 
of this code.