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.