GUI Components: Part 1 - Java: How to Program Early Objects - page 515

Java also provides interface MouseWheelListener to enable applications to respond to
the rotation of a mouse wheel . This interface declares method mouseWheelMoved , which
receives a MouseWheelEvent as its argument. Class MouseWheelEvent (a subclass of Mouse-
Event ) contains methods that enable the event handler to obtain information about the
amount of wheel rotation.

Tracking Mouse Events on a JPanel
The MouseTracker application (Figs. 12.28-12.29) demonstrates the MouseListener and
MouseMotionListener interface methods. The event-handler class (lines 36-97 of
Fig. 12.28) implements both interfaces. You must declare all seven methods from these two
interfaces when your class implements them both. Each mouse event in this example displays
a String in the JLabel called statusBar that is attached to the bottom of the window.

1 // Fig. 12.28: MouseTrackerFrame.java

2 // Mouse event handling.

3 import java.awt.Color;

4 import java.awt.BorderLayout;

5

import java.awt.event.MouseListener;

6

import java.awt.event.MouseMotionListener;

7

import java.awt.event.MouseEvent;

8 import javax.swing.JFrame;

9 import javax.swing.JLabel;

10 import javax.swing.JPanel;

11
12 public class MouseTrackerFrame extends JFrame

13 {

14 private final JPanel mousePanel; // panel in which mouse events occur

15 private final JLabel statusBar; // displays event information

16
17 // MouseTrackerFrame constructor sets up GUI and

18 // registers mouse event handlers

19 public MouseTrackerFrame()

20 {

21 super ( "Demonstrating Mouse Events" );

22
23 mousePanel = new JPanel();

mousePanel.setBackground( Color.WHITE );
add(mousePanel, BorderLayout.CENTER ); // add panel to JFrame

24

25

26
27 statusBar = new JLabel( "Mouse outside JPanel") ;

add(statusBar, BorderLayout.SOUTH ); // add label to JFrame 28

29
30 // create and register listener for mouse and mouse motion events

MouseHandler handler = new MouseHandler();
mousePanel.addMouseListener(handler);
mousePanel.addMouseMotionListener(handler);

31

32

33

34 }

35

Fig. 12.28 | Mouse event handling. (Part 1 of 3.)