Java Reference
In-Depth Information
Method
Description
Receives intermediate results from the
publish
method and processes
these results on the event dispatch thread.
process
setProgress
Sets the progress property to notify any property change listeners on the
event dispatch thread of progress bar updates.
Fig. 23.23
|
Commonly used
SwingWorker
methods. (Part 2 of 2.)
Numbers
In the next example, the user enters a number
n
and the program gets the
n
th Fibonacci
number, which we calculate using the recursive algorithm discussed in Section 18.5. Since
the algorithm is time consuming for large values, we use a
SwingWorker
object to perform
the calculation in a worker thread. The GUI also provides a separate set of components
that get the next Fibonacci number in the sequence with each click of a button, beginning
with
fibonacci(1).
This set of components performs its short computation directly in
the event dispatch thread. This program is capable of producing up to the 92nd Fibonacci
number—subsequent values are outside the range that can be represented by a
long
. Recall
that you can use class
BigInteger
to represent arbitrarily large integer values.
Class
BackgroundCalculator
(Fig. 23.24) performs the recursive Fibonacci calcula-
tion in a
worker thread
. This class extends
SwingWorker
(line 8), overriding the methods
doInBackground
and
done
. Method
doInBackground
(lines 21-24) computes the
n
th
Fibonacci number in a worker thread and returns the result. Method
done
(lines 27-43)
displays the result in a
JLabel
.
1
// Fig. 23.24: BackgroundCalculator.java
2
// SwingWorker subclass for calculating Fibonacci numbers
3
// in a background thread.
4
import
javax.swing.SwingWorker;
5
import
javax.swing.JLabel;
6
import
java.util.concurrent.ExecutionException;
7
8
public class
BackgroundCalculator
extends
SwingWorker<Long, Object>
9
{
10
private final int
n;
// Fibonacci number to calculate
11
private final
JLabel resultJLabel;
// JLabel to display the result
12
13
// constructor
14
public
BackgroundCalculator(
int
n, JLabel resultJLabel)
15
{
16
this
.n = n;
17
this
.resultJLabel = resultJLabel;
18
}
Fig. 23.24
|
SwingWorker
subclass for calculating Fibonacci numbers in a background thread.
(Part 1 of 2.)
