Java Reference
In-Depth Information
7
public
static
void
main(String[] args)
8
{
9
DrawPanel panel =
new
DrawPanel();
10
JFrame app =
new
JFrame();
11
12
app.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE
);
13
app.add(panel);
14
app.setSize(
300
,
300
);
15
app.setVisible(
true
);
16
}
17
}
// end class TestDraw
Fig. 8.19
|
Creating a
JFrame
to display a
DrawPanel
. (Part 2 of 2.)
GUI and Graphics Case Study Exercise
8.1
Extend the program in Figs. 8.17-8.19 to randomly draw rectangles and ovals. Create classes
MyRectangle
and
MyOval
. Both of these classes should include
x1
,
y1
,
x2
,
y2
coordinates, a color and a
boolean
flag to determine whether the shape is filled. Declare a constructor in each class with argu-
ments for initializing all the instance variables. To help draw rectangles and ovals, each class should
provide methods
getUpperLeftX
,
getUpperLeftY
,
getWidth
and
getHeight
that calculate the upper-
left
x
-coordinate, upper-left
y
-coordinate, width and height, respectively. The upper-left
x
-coordinate
is the smaller of the two
x
-coordinate values, the upper-left
y
-coordinate is the smaller of the two
y
-
coordinate values, the width is the absolute value of the difference between the two
x
-coordinate val-
ues, and the height is the absolute value of the difference between the two
y
-coordinate values.
Class
DrawPanel
, which extends
JPanel
and handles the creation of the shapes, should declare
three arrays, one for each shape type. The length of each array should be a random number
between 1 and 5. The constructor of class
DrawPanel
will fill each array with shapes of random
position, size, color and fill.
In addition, modify all three shape classes to include the following:
a)
A constructor with no arguments that sets the shape's coordinates to
0
, the color of the
shape to
Color.BLACK
, and the filled property to
false
(
MyRectangle
and
MyOval
only).
b)
Set
methods for the instance variables in each class. The methods that set a coordinate
value should verify that the argument is greater than or equal to zero before setting the
coordinate—if it's not, they should set the coordinate to zero. The constructor should
call the
set
methods rather than initialize the local variables directly.
c)
Get
methods for the instance variables in each class. Method
draw
should reference the
coordinates by the
get
methods rather than access them directly.
