JProgress Bar Indeterminate mode not updating - swing

Question

I have a JNI function that can take a while to complete, and I want a JProgress bar in indeterminate mode running while it is finishing the function. I have read the tutorials provided by Oracle, but the nature of their tutorials doesn't seem to help me understand how to do it. I realize that I should be running this function in a background thread, but I'm not quite sure how to do it.
Here is relevant code. I have a button (runButton) that will call the function, mainCpp(), when pressed:
public class Foo extends javax.swing.JFrame
implements ActionListener,
PropertyChangeListener{
#Override
public void actionPerformed(ActionEvent ae){
//Don't know what goes here, I don't think it is necessary though because I do not intend to use a determinate progress bar
}
#Override
public void propertyChange(PropertyChangeEvent pce){
//I don't intend on using an determinate progress bar, so I also do not think this is necassary
}
class Task extends SwingWorker<Void, Void>{
#Override
public Void doInBackground{
Foo t = new Foo();
t.mainCpp();
System.out.println("Done...");
}
return null;
}
/*JNI Function Declaration*/
public native int mainCpp(); //The original function takes arguments, but I have ommitted them for simplicity. If they are part of the problem, I can put them back in.
...//some codes about GUI
private void runButtonActionPerformed(java.awt.event.ActionEvent evt) {
ProgressBar.setIndeterminate(true);
Task task = new Task();
task.execute();
ProgressBar.setIndeterminate(false);
}
/*Declarations*/
private javax.swing.JButton runButton;
}
Any help would be appreciated.
EDIT: Editted in an attempt to do what kiheru suggested, but still does not work.

Answer 1

Assuming you have a SwingWorker like this:
class Task extends SwingWorker<Void, Void>{
#Override
public Void doInBackground() {
// I'm not sure of the code snippets if you are already in a
// Foo instance; if this is internal to Foo then you obviously do
// not need to create another instance, but just call mainCpp().
Foo t = new Foo();
t.mainCpp();
return null;
}
#Override
public void done()
// Stop progress bar, etc
...
}
}
You can either keep an instance in a field of the containing object, and then using it would work like this:
private void runButtonActionPerformed(java.awt.event.ActionEvent evt) {
// Start progress bar, disable the button, etc.
...
// Task task has been created earlier, maybe in the constructor
task.execute();
}
, or you can create a worker in place:
private void runButtonActionPerformed(java.awt.event.ActionEvent evt) {
// Start progress bar, disable the button, etc.
...
new Task().execute();
}