Java Reference
In-Depth Information
19
20
// long-running code to be run in a worker thread
21
public
Long doInBackground()
22
{
23
return
nthFib = fibonacci(n);
24
}
25
26
// code to run on the event dispatch thread when doInBackground returns
27
protected void
done()
28
{
29
try
30
{
31
// get the result of doInBackground and display it
resultJLabel.setText(get().toString());
32
33
}
34
catch
(InterruptedException ex)
35
{
36
resultJLabel.setText(
"Interrupted while waiting for results."
);
37
}
38
catch
(ExecutionException ex)
39
{
40
resultJLabel.setText(
41
"Error encountered while performing calculation."
);
42
}
43
}
44
45
// recursive method fibonacci; calculates nth Fibonacci number
46
public long
fibonacci(
long
number)
47
{
48
if
(number ==
0
|| number ==
1
)
49
return
number;
50
else
51
return
fibonacci(number -
1
) + fibonacci(number -
2
);
52
}
53
}
// end class BackgroundCalculator
Fig. 23.24
|
SwingWorker
subclass for calculating Fibonacci numbers in a background thread.
(Part 2 of 2.)
SwingWorker
is a
generic class
. In line 8, the first type parameter is
Long
and the second
is
Object
. The first type parameter indicates the type returned by the
doInBackground
method; the second indicates the type that's passed between the
publish
and
process
methods to handle intermediate results. Since we do not use
publish
and
process
in this
example, we simply use
Object
as the second type parameter. We discuss
publish
and
process
in Section 23.11.2.
A
BackgroundCalculator
object can be instantiated from a class that controls a GUI.
A
BackgroundCalculator
maintains instance variables for an integer that represents the
Fibonacci number to be calculated and a
JLabel
that displays the results of the calculation
(lines 10-11). The
BackgroundCalculator
constructor (lines 14-18) initializes these
instance variables with the arguments that are passed to the constructor.
