ActionListener problem

Question

I have a problem with my actionListener. It seems that the actionListener runs automatically before I click the button? The "This should not appear in the console before button click" appear in the console before I click the button".... This is strange.

.... 
button1.addActionListener(this); 
button2.addActionListener(this);
....
public void actionPerformed(ActionEvent e) {

   System.out.println("This should not appear in the console before button click");

   if (e.getSource()==button1)
      System.out.println ("answer1");

   else if (e.getSource()==button2)
      System.out.println ("answer2");
   .....
}

Answer 1

You can tell where methods are being called from by calling Thread.dumpStack(). That will print the stack trace to the error stream (possibly the Java console). Alternatively use a debugger and place a break point on the first line of the method.

public void actionPerformed(ActionEvent e) {
   Thread.duumpStack();
   System.out.println("This should not appear in the console before button click");
   ...

BTW: I recommend not using EventObject.getSource. Instead add a new listener for every action.

So your example code would become:

button1.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent event) {
        System.out.println("answer1");
    } 
});
button2.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent event) {
        System.out.println("answer2");
    } 
});

Unfortunately the boilerplate associated with anonymous inner classes is distinctly verbose, but the intention is clearer.

Answer 2

Also make sure that you have not added 'this' as an ActionListener to any other components that might be use before you click either of the buttons. You could also search your code for doClick() calls to make sure you dont call it programatically.