Java Reference
In-Depth Information
downButton =
new
JRadioButton(
"Decrement"
,
true
);
p. add(upButton) ;
p . add(downButton) ;
ButtonGroup group =
new
ButtonGroup () ;
group .add(upButton) ;
group .add(downButton) ;
CenterPanel centerPanel =
new
CenterPanel () ;
add(centerPanel , BorderLayout .CENTER) ;
}
class
CenterPanel
extends
JPanel
{
JTextField textField =
new
JTextField(
"0"
, 20) ;
int
x=0;
public
CenterPanel ()
{
add(textField);
Timer t =
new
Timer(1000,
new
ActionListener ()
{
public void
actionPerformed(ActionEvent e)
{
if
(upButton . isSelected () ) x++;
if
(downButton. isSelected()) x
−−
;
textField .setText(
""
+x);
}
}
);
t. start() ;
textField . getDocument() . addDocumentListener(
new
DocumentListener
()
{
public void
insertUpdate(DocumentEvent e)
{
try
{
x = Integer . parseInt(textField .getText() . trim()) ;
}
catch
(Exception es)
{
}
}
public void
removeUpdate(DocumentEvent e )
{
try
{
x = Integer . parseInt(textField .getText() . trim()) ;
}
catch
(Exception es)
{
}
}
public void
changedUpdate(DocumentEvent e)
{
}
}
);
}
}
}
The program stores a variable
x
, which is displayed in the text field. A timer that changes
the value of
x
every second is created. The
isSlected
method checks which radio button
is selected. Depending on the outcome, the value of
x
is incremented or decremented by
one. The user can also manually change the value of
x
. Every time something is inserted in
or deleted from the text field, a method is called. In both cases, the variable
x
is updated
to the new value of the text field. Note that the
parseInt
method is used to convert a
string to an integer. If the user does not type in an integer, then an exception is raised.
The
try-catch
blocks guarantee that in this situation the program simply continues to
increment or decrement the value
x
and disregards the user input.
