Java Reference
In-Depth Information
10
// create frame for ColorJPanel
11
JFrame frame =
new
JFrame(
"Using colors"
);
12
frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE
);
13
14
ColorJPanel colorJPanel =
new
ColorJPanel();
15
frame.add(colorJPanel);
16
frame.setSize(
400
,
180
);
17
frame.setVisible(
true
);
18
}
19
}
// end class ShowColors
Fig. 13.6
|
Demonstrating
Color
s. (Part 2 of 2.)
Line 19 uses
Graphics
method
drawString
to draw a
String
in the current color.
The expression
g.getColor()
retrieves the current color from the
Graphics
object. We
then concatenate the
Color
with string
"Current RGB: "
, resulting in an
implicit
call to
class
Color
's
toString
method. The
String
representation of a
Color
contains the class
name and package (
java.awt.Color
) and the red, green and blue values.
Look-and-Feel Observation 13.1
People perceive colors differently. Choose your colors carefully to ensure that your applica-
tion is readable, both for people who can perceive color and for those who are color blind.
Try to avoid using many different colors in close proximity.
Lines 22-24 and 27-29 perform the same tasks again. Line 22 uses the
Color
con-
structor with three
float
arguments to create a dark green color (
0.50f
for red,
0.75f
for
green and
0.0f
for blue). Note the syntax of the values. The letter
f
appended to a
floating-point literal indicates that the literal should be treated as type
float
. Recall that
by default, floating-point literals are treated as type
double
.
Line 27 sets the current drawing color to one of the predeclared
Color
constants
(
Color.BLUE
). The
Color
constants are
static
, so they're created when class
Color
is
loaded into memory at execution time.
The statement in lines 35-36 makes calls to
Color
methods
getRed
,
getGreen
and
getBlue
on the predeclared
Color.MAGENTA
constant. Method
main
of class
ShowColors
(lines 8-18 of Fig. 13.6) creates the
JFrame
that will contain a
ColorJPanel
object where
the colors will be displayed.
Software Engineering Observation 13.1
To change the color, you must create a new
Color
object (or use one of the predeclared
Color
constants). Like
String
objects,
Color
objects are immutable (not modifiable).
