Action listener in different class

Question

Hi
I now have a class called Gui and a class called Listener.
The gui contains
public class Gui implements ActionListener
public void actionPerformed(ActionEvent e) { }the Listener contains
public class Listener extends gui implements ActionListener
public void actionPerformed(ActionEvent e)
{ System.out.println("test");     }The problem i have is how to destinct from which button is pressed or which comboBoxItem is pressed?
when i do :
if((e.getSource()).equals(btn1))I get a nullPointerException.
btn1 is defined to be protected in the class gui and is implemented:
btn.addActionListener(al);
where al is Listener al = new Listener(); created in the gui constructer.
Anyone that could help me out with how to determind which button is pressed?
Thanks

Answer 1

Re: readability - I completely agree that this is a very important issue and I conceded a wee hip-and-yip-yip hooray to your tutor /instructor. From what I read on these boards, it is something of a breath of frsh air to hear of such enlightened teaching - however ...
I don't see an argument here. I agree that in a big GUI build that naming your GUI something like;-
public class MyMainGUI extends JFrame implements ActionListener{
... is a bit ugly, however IMO:-
class ButtonListener implements ActionListener{
... is highly readable and clear
My personal preference is then to do this;-
class ButtonListener implements ActionListener{
public void actionPerformed(ActionEvent ae){
String action = ae.getActionCommand();
if(action.equals("blah")) doThis();
if(action.equals("blahBlah")) doThat();
... where doThis(); and doThat(); are method calls, ie: outside the CustomListenerClass - this maintains the structure and clarity. The problem with 'external classes' is that you often need to pass on variables in the constructor and sometimes you cannot access (or change) the variables in the MainGUI class without making variables and /or getter & setter methods static, which can be something of a counterflow to good OOP design.