Review of actionPerformed()

The parameter for actionPerformed() is a reference to an ActionEvent object. When the button is clicked, the method is called with a new action object parameter. So far, we've not used the ActionEvent object. You will see this shortly. Here is the picture of what is happening:

Usually the registered ActionListener is the same object as the frame that holds the button. Usually this is an object that derives from the Swing JFrame class. (In other words, you define a class based on JFrame. The class contains a button and implements the ActionListener interface).