GUI Components: Part 1 - Java: How to Program Early Objects - page 525

9 public static void main(String[] args)

10 {

11 // create JFrame

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JFrame application = new JFrame( "A simple paint program" );

13
14

PaintPanel paintPanel = new PaintPanel();

15

application.add(paintPanel, BorderLayout.CENTER );

16
17

// create a label and place it in SOUTH of BorderLayout

18

application.add( new JLabel( "Drag the mouse to draw") ,

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BorderLayout.SOUTH );

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application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

22

application.setSize( 400 , 200 );

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application.setVisible( true );

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}

25

} // end class Painter

Fig. 12.35 | Testing PaintPanel . (Part 2 of 2.)

12.17 Key Event Handling
This section presents the KeyListener interface for handling key events . Key events are
generated when keys on the keyboard are pressed and released. A class that implements
KeyListener must provide declarations for methods keyPressed , keyReleased and key-
Typed , each of which receives a KeyEvent as its argument. Class KeyEvent is a subclass of
InputEvent . Method keyPressed is called in response to pressing any key. Method key-
Typed is called in response to pressing any key that is not an action key . (The action keys
are any arrow key, Home , End , Page Up , Page Down , any function key, etc.) Method key-
Released is called when the key is released after any keyPressed or keyTyped event.
The application of Figs. 12.36-12.37 demonstrates the KeyListener methods. Class
KeyDemoFrame implements the KeyListener interface, so all three methods are declared in
the application. The constructor (Fig. 12.36, lines 17-28) registers the application to
handle its own key events by using method addKeyListener at line 27. Method addKey-
Listener is declared in class Component , so every subclass of Component can notify Key-
Listener objects of key events for that Component .

1 // Fig. 12.36: KeyDemoFrame.java

2 // Key event handling.

3 import java.awt.Color;

Fig. 12.36 | Key event handling. (Part 1 of 3.)