Question on event listeners ..

Hi,

I'm learning Java and have understood that you have to 'implement' any listeners in the class definition to be able to use them.

ie public class ChangeTitle extends JFrame implements ActionListener

I have just entered and run a book example that implements the ActionListener event handler, but not only does the class use the 'addActionListener' method in the class constructor, but in the main() definition for the class it ALSO uses 'addWindowListener' ?????

How can this class use the WindowListener if hasn't 'implemented' it in the class definition.

ie shouldn't the class definition should be ;

public class ChangeTitle extends JFrame implements ActionListener, WindowListener

instead of

public class ChangeTitle extends JFrame implements ActionListener

The small program compiles and runs okay.