Swing - Update Label

Question

I have a message label and a submit button. The submit button will be pressed multiple times, and the action for the each press can take up to a minute.

When the button is pressed, I want to set the message to empty, and after the task is complete, I want to set the message to "Complete".

private void submitActionPerformed(java.awt.event.ActionEvent evt) {
   message = "";
   updateMessageLabel();

   doTheTask();

   /* this update is apply to the label after completion */
   message = "Complete";
}

Is it possible to update that message label before the submitActionPerformed() method is run (or in the method), but after the the button is clicked?

Answer 1

Although the Swing concurrency tutorial already contains some very good samples on how to deal with concurrency in Swing, find below an example which

• contains a checkbox to prove the UI is still alive
• has a progress bar, which gets updated from the SwingWorker

• has a label, which gets updated once the SwingWorker is finished

  import javax.swing.JCheckBox;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JProgressBar;
  import javax.swing.SwingWorker;
  import java.awt.BorderLayout;
  import java.awt.EventQueue;
  import java.lang.reflect.InvocationTargetException;
  import java.util.List;
  import java.util.concurrent.ExecutionException;
  
  public class SwingWorkerExample {
    private static JProgressBar PROGRESS_BAR;
    private static JLabel OUTPUT_LABEL;
    private static JFrame createGUI(){
      JFrame testFrame = new JFrame( "TestFrame" );
  
      PROGRESS_BAR = new JProgressBar(  );
      PROGRESS_BAR.setMinimum( 0 );
      PROGRESS_BAR.setMaximum( 100 );
  
      OUTPUT_LABEL = new JLabel( "Processing" );
  
      testFrame.getContentPane().add( PROGRESS_BAR, BorderLayout.CENTER );
      testFrame.getContentPane().add( OUTPUT_LABEL, BorderLayout.SOUTH );
  
      //add a checkbox as well to proof the UI is still responsive
      testFrame.getContentPane().add( new JCheckBox( "Click me to proof UI is responsive" ), BorderLayout.NORTH );
  
  
  
      testFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      return testFrame;
    }
  
    public static void main( String[] args ) throws InvocationTargetException, InterruptedException {
      EventQueue.invokeAndWait( new Runnable() {
        @Override
        public void run() {
          JFrame frame = createGUI();
  
          frame.pack();
          frame.setVisible( true );
        }
      } );
      //start the SwingWorker outside the EDT
      MySwingWorker worker = new MySwingWorker( PROGRESS_BAR, OUTPUT_LABEL );
      worker.execute();
    }
    private static class MySwingWorker extends SwingWorker<String, Double>{
      private final JProgressBar fProgressBar;
      private final JLabel fLabel;
      private MySwingWorker( JProgressBar aProgressBar, JLabel aLabel ) {
        fProgressBar = aProgressBar;
        fLabel = aLabel;
      }
  
      @Override
      protected String doInBackground() throws Exception {
        int maxNumber = 10;
        for( int i = 0; i < maxNumber; i++ ){
          Thread.sleep( 2000 );//simulate long running process
          double factor = ((double)(i+1) / maxNumber);
          System.out.println("Intermediate results ready");
          publish( factor );//publish the progress
        }
        return "Finished";
      }
  
      @Override
      protected void process( List<Double> aDoubles ) {
        //update the percentage of the progress bar that is done
        int amount = fProgressBar.getMaximum() - fProgressBar.getMinimum();
        fProgressBar.setValue( ( int ) (fProgressBar.getMinimum() + ( amount * aDoubles.get( aDoubles.size() - 1 ))) );
      }
  
      @Override
      protected void done() {
        try {
          fLabel.setText( get() );
        } catch ( InterruptedException e ) {
          e.printStackTrace();
        } catch ( ExecutionException e ) {
          e.printStackTrace();
        }
      }
    }
  }