Java Reference
In-Depth Information
The
Decrease
Level
button's event handler is registered in lines 60-80. Method
actionPerformed
retrieves the current level of recursion and decrements it by 1 (lines 67-
68). Lines 71-72 ensure that the level is greater than or equal to
MIN_LEVEL
and less than
or equal to
MAX_LEVEL
—the fractal is not defined for recursion levels less than
MIN_LEVEL
and you can't see the additional detail above
MAX_LEVEL
. You can go up to any desired
level, but around level 10 and higher, the fractal rendering becomes
slow
due to the details
to be drawn. Lines 74-76 reset the level label to reflect the change—the new level is set
and the
repaint
method is called to update the image to show the fractal at the new level.
The
Increase Level
JButton
works like the
Decrease Level
JButton
, but the level is
incremented rather than decremented to show more details of the fractal (lines 93-94).
When the application is first executed, the level will be set to 0, which will display a blue
line between two points that were specified in the
FractalJPanel
class.
Class
FractalJPanel
(Fig. 18.19) specifies the drawing
JPanel
's dimensions as
400
by
400
(lines 13-14). The
FractalJPanel
constructor (lines 18-24) takes the current level
as a parameter and assigns it to its instance variable
level
. Instance variable
color
is set
to blue by default. Lines 22-23 change the
JPanel
's background color to white (so the
fractal is easy to see), and set the drawing
FractalJPanel
's dimensions.
1
// Fig. 18.19: FractalJPanel.java
2
// Drawing the "Lo feather fractal" using recursion.
3
import
java.awt.Graphics;
4
import
java.awt.Color;
5
import
java.awt.Dimension;
6
import
javax.swing.JPanel;
7
8
public
class
FractalJPanel
extends
JPanel
9
{
10
private
Color color;
// stores color used to draw fractal
11
private
int
level;
// stores current level of fractal
12
13
private
static final
int
WIDTH
=
400
;
// defines width of JPanel
14
private
static final
int
HEIGHT
=
400
;
// defines height of JPanel
15
16
// set the initial fractal level to the value specified
17
// and set up JPanel specifications
18
public
FractalJPanel(
int
currentLevel)
19
{
20
color =
Color.BLUE
;
// initialize drawing color to blue
21
level = currentLevel;
// set initial fractal level
22
setBackground(
Color.WHITE
);
23
setPreferredSize(
new
Dimension(
WIDTH
,
HEIGHT
));
24
}
25
26
// draw fractal recursively
public
void
drawFractal(
int
level,
int
xA,
int
yA,
int
xB,
int
yB, Graphics g)
{
27
28
29
Fig. 18.19
|
Drawing the “Lo feather fractal” using recursion. (Part 1 of 4.)
