问不显示JProgressBar

EN

JFrame progressFrame = new JFrame();
JProgressBar progressBar = new JProgressBar();
progressBar.setIndeterminate(true);
progressBar.setString(selectedFiles[i].getName() + "is being processed ...");
progressFrame.setSize(400, 200);
progressFrame.add(progressBar);
progressFrame.setVisible(true);
try
{
  Thread.sleep(6000);
}
catch(Exception ex)
{ }
EvaluateLabsController.getInstance().evaluate(selectedFiles[i]);
progressBar.setIndeterminate(false);

progressFrame.setVisible(false);