Java Reference
In-Depth Information
Arcs
Using Java's graphics features, we can create complex drawings that would be more tedious
to code line by line. In Figs. 7.25-7.26, we use arrays and repetition statements to draw a
rainbow by using
Graphics
method
fillArc
. Drawing arcs in Java is similar to drawing
ovals—an arc is simply a section of an oval.
In Fig. 7.25, lines 10-11 declare and create two new color constants—
VIOLET
and
INDIGO
. As you may know, the colors of a rainbow are red, orange, yellow, green, blue,
indigo and violet. Java has predefined constants only for the first five colors. Lines 15-17
initialize an array with the colors of the rainbow, starting with the innermost arcs first. The
array begins with two
Color.WHITE
elements, which, as you'll soon see, are for drawing the
empty arcs at the center of the rainbow. The instance variables can be initialized when
they're declared, as shown in lines 10-17. The constructor (lines 20-23) contains a single
statement that calls method
setBackground
(which is inherited from class
JPanel
) with
the parameter
Color.WHITE
. Method
setBackground
takes a single
Color
argument and
sets the background of the component to that color.
1
// Fig. 7.25: DrawRainbow.java
2
// Drawing a rainbow using arcs and an array of colors.
3
import
java.awt.Color;
4
import
java.awt.Graphics;
5
import
javax.swing.JPanel;
6
7
public
class
DrawRainbow
extends
JPanel
8
{
9
// define indigo and violet
10
private final static
Color
VIOLET
=
new
Color(
128
,
0
,
128
);
11
private final static
Color
INDIGO
=
new
Color(
75
,
0
,
130
);
12
13
// colors to use in the rainbow, starting from the innermost
14
// The two white entries result in an empty arc in the center
15
private
Color[] colors =
16
{
Color.WHITE
,
Color.WHITE
,
VIOLET
,
INDIGO
,
Color.BLUE
,
17
Color.GREEN
,
Color.YELLOW
,
Color.ORANGE
,
Color.RED
};
18
19
// constructor
20
public
DrawRainbow()
21
{
22
setBackground(
Color.WHITE
);
// set the background to white
23
}
24
25
// draws a rainbow using concentric arcs
26
public
void
paintComponent(Graphics g)
27
{
28
super
.paintComponent(g);
29
30
int
radius =
20
;
// radius of an arc
31
Fig. 7.25
|
Drawing a rainbow using arcs and an array of colors. (Part 1 of 2.)
