Java™ How To Program (Early Objects), Tenth Edition

Registering the Event Handler for Each Text Field

In the TextFieldFrame constructor, line 42 creates a TextFieldHandler object and assigns it to variable handler. This object’s actionPerformed method will be called automatically when the user presses Enter in any of the GUI’s text fields. However, before this can occur, the program must register this object as the event handler for each text field. Lines 43–46 are the event-registration statements that specify handler as the event handler for the three JTextFields and the JPasswordField. The application calls JTextField method addActionListener to register the event handler for each component. This method receives as its argument an ActionListener object, which can be an object of any class ...