EVENT-DRIVEN PROGRAMMING - Introduction to Java Programming - page 620

message at the mouse point. When you move the mouse without pressing a button, the
mouseMoved method is invoked. Because the listener is interested only in the mouse-dragged
event, the mouseDragged method is implemented (lines 36-41).
The mouseDragged method is invoked when you move the mouse with a button pressed.
This method obtains the mouse location using the getX and getY methods (lines 38-39) in
the MouseEvent class. This becomes the new location for the message. Invoking the
repaint() method (line 40) causes paintComponent to be invoked (line 50), which dis-
plays the message in a new location.

16.14 What method do you use to get the mouse-point position for a mouse event?
16.15 What is the listener interface for mouse pressed, released, clicked, entered, and
exited? What is the listener interface for mouse moved and dragged?

✓ ✓

Check

Point

16.9 Listener Interface Adapters
A listener interface adapter is a class that provides the default implementation for all
the methods in the listener interface.

Key
Point

Because the methods in the MouseMotionListener interface are abstract, you must imple-
ment all of them even if your program does not care about some of the events. Java provides
support classes, called listener interface adapters , that provide default implementations for all
the methods in the listener interface. The default implementation is simply an empty body. Java
provides listener interface adapters for every AWT listener interface with multiple handlers. A
listener interface adapter is named X Adapter for X Listener. For example, MouseMotionAdapter
is a listener interface adapter for MouseMotionListener . Table 16.2 lists some listener inter-
face adapters used in this topic.

listener interface adapter

T ABLE 16.2 Listener Interface Adapters

Adapter Interface

MouseListener

MouseAdapter

MouseMotionAdapter MouseMotionListener

KeyAdapter KeyListener

WindowAdapter WindowListener

Using MouseMotionAdapter , the code in lines 34-46 in Listing 16.8 (shown in (a)) can
be replaced by the following code, as shown in (b).

addMouseMotionListener(
new MouseMotionListener() {
@Override /** Handle mouse-dragged event */
public void mouseDragged(MouseEvent e){
x = e.getX();
y = e.getY();
repaint();

addMouseMotionListener(
new {
@Override /** Handle mouse-dragged event */
public void mouseDragged(MouseEvent e){
x = e.getX();
y = e.getY();
repaint();

MouseMotionAdapter()

} }

});

@Override /** Handle mouse-moved event */
public void mouseMoved(MouseEvent e) {
}
});

(a) Using a listener interface (b) Using a listener interface adapter