Java Reference
In-Depth Information
To see how the delegation model works in practice, we will look at an example that
handles one of the most commonly used event generators: the mouse. The example will
show how to handle the basic mouse and mouse motion events. (Note that it is also possible
to handle mouse wheel events, but this is left to you as an exercise.)
Handling Mouse and Mouse Motion Events
To handle mouse and mouse motion events, you must implement the
MouseListener
and
the
MouseMotionListener
interfaces. The
MouseListener
interface defines five methods.
If a mouse button is clicked,
mouseClicked( )
is invoked. When the mouse enters a com-
ponent, the
mouseEntered( )
method is called. When it leaves,
mouseExited( )
is called.
The
mousePressed( )
and
mouseReleased( )
methods are invoked when a mouse button is
pressed and released, respectively. The general forms of these methods are shown here:
void mouseClicked(MouseEvent
me
)
void mouseEntered(MouseEvent
me
)
void mouseExited(MouseEvent
me
)
void mousePressed(MouseEvent
me
)
void mouseReleased(MouseEvent
me
)
The
MouseMotionListener
interface defines two methods. The
mouseDragged( )
method is called multiple times as the mouse is dragged. The
mouseMoved( )
method is
called multiple times as the mouse is moved. Their general forms are shown here:
void mouseDragged(MouseEvent
me
)
void mouseMoved(MouseEvent
me
)
The
MouseEvent
object passed in
me
describes the event.
MouseEvent
defines a num-
ber of methods that you can use to get information about what happened. Possibly the most
commonly used methods in
MouseEvent
are
getX( )
and
getY( )
. These return the X and
Y coordinates of the mouse (relative to the window) when the event occurred. Their forms
are shown here:
int getX( )
int getY( )
