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b) The first argument to the constructor should be
SwingConstants.HORIZONTAL
or
Swing-
Constants.VERTICAL
, and the keyword
new
must be used after the
=
operator. Also, the
minimum value should be less than the maximum and the initial value should be in range.
c) The constant should be either
BOTH
,
HORIZONTAL
,
VERTICAL
or
NONE
.
d)
paintcomponent
should be
paintComponent
, and the method should call
super.paint-
Component(g)
as its first statement.
e)
The
JFrame
's
setSize
method must also be called to establish the size of the window.
Exercises
22.4
(Fill-in-the-Blanks)
Fill in the blanks in each of the following statements:
a)
A
JMenuItem
that is a
JMenu
is called a(n)
.
b) Method attaches a
JMenuBar
to a
JFrame
.
c) Container class has a default
BoxLayout
.
d) A(n) manages a set of child windows declared with class
JInternalFrame
.
22.5
(True or False)
State whether each of the following is
true
or
false
. If
false
, explain why.
a) Menus require a
JMenuBar
object so they can be attached to a
JFrame
.
b)
BoxLayout
is the default layout manager for a
JFrame
.
c)
JApplet
s can contain menus.
22.6
(Find the Code Errors)
Find the error(s) in each of the following. Explain how to correct
the error(s).
a)
x.add(
new
JMenuItem(
"Submenu Color"
));
// create submenu
b)
container.setLayout(
new
GridbagLayout());
22.7
(Display a Circle and Its Attributes)
Write a program that displays a circle of random size
and calculates and displays the area, radius, diameter and circumference. Use the following equa-
tions:
diameter =
2
× radius
,
area =
π
π
× radius
2
,
circumference =
2
×
× radius
. Use the constant
π
Math.PI
for pi (
). All drawing should be done on a subclass of
JPanel
, and the results of the calcu-
lations should be displayed in a read-only
JTextArea
.
22.8
(Using a
JSlider
)
Enhance the program in Exercise 22.7 by allowing the user to alter the
radius with a
JSlider
. The program should work for all radii in the range from 100 to 200. As the
radius changes, the diameter, area and circumference should be updated and displayed. The initial
radius should be 150. Use the equations from Exercise 22.7. All drawing should be done on a sub-
class of
JPanel
, and the results of the calculations should be displayed in a read-only
JTextArea
.
22.9
(Varying
weightx
and
weighty
)
Explore the effects of varying the
weightx
and
weighty
values of the program in Fig. 22.21. What happens when a slot has a nonzero weight but is not al-
lowed to fill the whole area (i.e., the
fill
value is not
BOTH
)?
22.10
(Synchronizing a
JSlider
and a
JTextField
)
Write a program that uses the
paintCompo-
nent
method to draw the current value of a
JSlider
on a subclass of
JPanel
. In addition, provide a
JTextField
where a specific value can be entered. The
JTextField
should display the current value
of the
JSlider
at all times. Changing the value in the
JTextField
should also update the
JSlider
.
A
JLabel
should be used to identify the
JTextField
. The
JSlider
methods
setValue
and
getValue
should be used. [
Note:
The
setValue
method is a
public
method that does not return a value and
takes one integer argument, the
JSlider
value, which determines the position of the thumb.]
22.11
(Creating a Color Chooser)
Declare a subclass of
JPanel
called
MyColorChooser
that pro-
vides three
JSlider
objects and three
JTextField
objects. Each
JSlider
represents the values from
0 to 255 for the red, green and blue parts of a color. Use these values as the arguments to the
Color
constructor to create a new
Color
object. Display the current value of each
JSlider
in the corre-
