Java Reference
In-Depth Information
116
southJPanel.add(cancelJButton);
117
progressJProgressBar.setStringPainted(
true
);
118
southJPanel.add(progressJProgressBar);
119
southJPanel.add(statusJLabel);
120
121
add(northJPanel,
BorderLayout.NORTH
);
122
add(southJPanel,
BorderLayout.SOUTH
);
123
setSize(
350
,
300
);
124
setVisible(
true
);
125
}
// end constructor
126
127
// main method begins program execution
128
public static void
main(String[] args)
129
{
130
FindPrimes application =
new
FindPrimes();
131
application.setDefaultCloseOperation(
EXIT_ON_CLOSE
);
132
}
// end main
133
}
// end class FindPrimes
Fig. 23.27
|
Using a
SwingWorker
to display prime numbers and update a
JProgressBar
while the prime numbers are being calculated. (Part 4 of 4.)
Lines 42-94 register the event handler for the
getPrimesJButton
. When the user
clicks this
JButton
, lines 47-49 reset the
JProgressBar
and clear the
displayPrimes-
JTextArea
and the
statusJLabel
. Lines 53-63 parse the value in the
JTextField
and dis-
play an error message if the value is not an integer. Lines 66-68 construct a new
PrimeCalculator
object, passing as arguments the integer the user entered, the
display-
PrimesJTextArea
for displaying the primes, the
statusJLabel
and the two
JButton
s.
Lines 71-85 register a
PropertyChangeListener
for the
PrimeCalculator
object.
PropertyChangeListener
is an interface from package
java.beans
that defines a single
method,
propertyChange
. Every time method
setProgress
is invoked on a
PrimeCalcu-
lator
, the
PrimeCalculator
generates a
PropertyChangeEvent
to indicate that the prog-
ress property has changed. Method
propertyChange
listens for these events. Line 78 tests
whether a given
PropertyChangeEvent
indicates a change to the progress property. If so,
line 80 gets the new value of the property and line 81 updates the
JProgressBar
with the
new progress property value.
The
Get Primes
JButton
is disabled (line 88) so only one calculation that updates the
GUI can execute at a time, and the
Cancel
JButton
is enabled (line 89) to allow the user
