Java Reference
In-Depth Information
6
import
java.awt.event.MouseMotionAdapter;
7
import
java.util.ArrayList;
8
import
javax.swing.JPanel;
9
10
public
class
PaintPanel
extends
JPanel
11
{
12
// list of Point references
13
private final
ArrayList<Point> points =
new
ArrayList<>();
14
15
// set up GUI and register mouse event handler
16
public
PaintPanel()
17
{
18
// handle frame mouse motion event
19
addMouseMotionListener(
20
new
MouseMotionAdapter()
// anonymous inner class
21
{
22
// store drag coordinates and repaint
23
@Override
24
public
void
mouseDragged(MouseEvent event)
25
{
26
points.add(
event.getPoint()
repaint();
// repaint JFrame
);
27
28
}
29
}
30
);
31
}
32
33
// draw ovals in a 4-by-4 bounding box at specified locations on window
34
@Override
35
public
void
paintComponent(Graphics g)
36
{
37
super
.paintComponent(g);
// clears drawing area
38
39
// draw all points
40
for
(Point point : points)
41
g.fillOval(
point.x, point.y
,
4
,
4
);
42
}
43
}
// end class PaintPanel
Fig. 12.34
|
Adapter class used to implement event handlers. (Part 2 of 2.)
Class
PaintPanel
(Fig. 12.34) extends
JPanel
to create the dedicated drawing area.
Class
Point
(package
java.awt
) represents an
x-y
coordinate. We use objects of this class
to store the coordinates of each mouse drag event. Class
Graphics
is used to draw. In this
example, we use an
ArrayList
of
Point
s (line 13) to store the location at which each mouse
drag event occurs. As you'll see, method
paintComponent
uses these
Point
s to draw.
Lines 19-30 register a
MouseMotionListener
to listen for the
PaintPanel
's mouse
motion events. Lines 20-29 create an object of an anonymous inner class that extends the
adapter class
MouseMotionAdapter
. Recall that
MouseMotionAdapter
implements
Mouse-
MotionListener
, so the
anonymous inner class
object is a
MouseMotionListener
. The
anonymous inner class inherits default
mouseMoved
and
mouseDragged
implementations,
so it already implements all the interface's methods. However, the default implementa-
