SwingWorker example code
To: comp.lang.java.gui
Hello
I came up with an example program that uses all the methods in the new
SwingWorker class in Java 6. Thought it might be helpful.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
public class SwingWorkerExample extends JFrame
implements ActionListener {
private final JButton startButton, stopButton;
JScrollPane scrollPane = new JScrollPane();
private JList listBox = null;
private DefaultListModel listModel = new DefaultListModel();
private final JProgressBar progressBar;
private mySwingWorker swingWorker;
public SwingWorkerExample(){
super ("SwingWorkerExample");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
getContentPane().setLayout(new GridLayout(2, 2));
startButton = makeButton("Start");
stopButton = makeButton("Stop");
stopButton.setEnabled(false);
progressBar = makeProgressBar(0, 99);
listBox = new JList (listModel);
scrollPane.setViewportView (listBox);
getContentPane().add (scrollPane);
//Display the window.
pack();
setVisible(true);
}
// Class SwingWorker<T,V>
// T - the result type returned by this SwingWorker's doInBackground
and get methods
// V - the type used for carrying out intermediate results by this
SwingWorker's publish and process methods
private class mySwingWorker extends
javax.swing.SwingWorker<ArrayList<Integer>, Integer> {
// The first template argument, in this case, ArrayList<Integer>, is
what
// is returned by doInBackground(), and by get().
//
// The second template argument, in this case, Integer, is what
// is published with the publish method. It is also the data
// type which is stored by the java.util.List that is the parameter
// for the process method, which recieves the information published
// by the publish method.
protected ArrayList<Integer> doInBackground(){
// Returns items of the type given as the first template
// argument to the SwingWorker class.
if ( javax.swing.SwingUtilities.isEventDispatchThread() )
System.out.println("javax.swing.SwingUtilities.isEventDispatchThread()
returned true.");
Integer tmpValue = new Integer (1);
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 100; i++){
for (int j = 0; j < 100; j++){ // find every 100th prime, just to
make it slower
tmpValue = FindNextPrime (tmpValue.intValue());
// isCancelled() returns true if the cancel() method
// is invoked on this class. That is the proper way
// to stop this thread. See the actionPerformed
// method.
if (isCancelled()){
System.out.println("isCancelled");
return list;
}
}
// Successive calls to publish are coalesced into a
java.util.List,
// which is what is received by process, which in this case, is
used
// to update the JProgressBar. Thus, the values passed to publish
// range from 1 to 100.
publish (new Integer (i) );
list.add (tmpValue);
}
return list;
}
// Note, always use java.util.List here, or it will use the wrong
list.
protected void process(java.util.List<Integer> progressList) {
// This method is processing a java.util.List of items
// given as successive arguments to the publish method.
// Note that these calls are coalesced into a java.util.List.
// This list holds items of the type given as the
// second template parameter type to SwingWorker.
// Note that the get method below has nothing to do
// with the SwingWorker get method; it is the List's
// get method.
// This would be a good place to update a progress bar.
if ( !javax.swing.SwingUtilities.isEventDispatchThread() )
System.out.println("javax.swing.SwingUtilities.isEventDispatchThread()
returned false.");
Integer percentComplete =
progressList.get(progressList.size() - 1);
progressBar.setValue (percentComplete.intValue());
}
protected void done() {
System.out.println("doInBackground is complete");
if ( !javax.swing.SwingUtilities.isEventDispatchThread() )
System.out.println("javax.swing.SwingUtilities.isEventDispatchThread()
returned false.");
try {
// Here, the SwingWorker's get method returns an item
// of the same type as specified as the first type parameter
// given to the SwingWorker class.
ArrayList<Integer> results = get();
for (Integer i : results)
listModel.addElement (i.toString());
//repaint();
} catch (Exception e){
System.out.println("Caught an exception: " + e);
}
}
boolean IsPrime( int num ) // Checks whether a number is prime
{
int i;
for( i=2; i<=num/2; i++ )
{
if( num%i == 0 )
return false;
}
return true;
}
protected Integer FindNextPrime( int num ) // Returns next prime
number from passed arg.
{
do
{
if( num % 2 == 0 )
num++;
else
num+=2;
} while( !IsPrime(num));
return new Integer (num);
}
}
private JButton makeButton(String caption) {
JButton b = new JButton(caption);
b.setActionCommand(caption);
b.addActionListener(this);
getContentPane().add(b);
return b;
}
private JProgressBar makeProgressBar (int min, int max){
JProgressBar progressBar = new JProgressBar();
progressBar.setMinimum (min);
progressBar.setMaximum (max);
progressBar.setStringPainted(true);
progressBar.setBorderPainted(true);
getContentPane().add (progressBar);
return progressBar;
}
public void actionPerformed(ActionEvent e) {
if ("Start" == e.getActionCommand()) {
startButton.setEnabled(false);
stopButton.setEnabled(true);
// Note that it creates a new instance of the SwingWorker-derived
// class. Never reuse an old one.
(swingWorker = new mySwingWorker()).execute(); // new
instance
} else if ("Stop" == e.getActionCommand()) {
startButton.setEnabled(true);
stopButton.setEnabled(false);
swingWorker.cancel(true); // causes isCancelled to return
true in doInBackground
swingWorker = null;
}
}
public static void main(String[] args) {
// Notice that it kicks it off on the event-dispatching
// thread, not the main thread.
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new SwingWorkerExample();
}
});
}
}
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