Question

blueButton.addActionListener(new blueButtonListner());

What happens when this code is entered?

What I think is Java compiler creates an object called blueButtonListner() and it becomes an input to (parameters for) addActionListener

If that is correct as I guessed then this code should also work:

redButton.addActionListener(rr);
redButtonListener rr =new redButtonListener();

But it shows an error. Can someone explain this to me?

Answer 1

It’s a matter if precedence, you can’t have something until it’s created

redButton.addActionListener(rr); redButtonListener rr =new redButtonListener();

Won’t work, because rr hasn’t been defined yet, the compiler has not idea of what it is.

In contrast

blueButton.addActionListener(new blueButtonListner())

The compiler creates a temporary Object and passes it to the addActionListener method.

You can correct your code with this

redButtonListener rr =new redButtonListener();
redButton.addActionListener(rr);