Question

I’m not a Java programmer and I’m not sure if what I’m doing is correct or not, or if exist a better way to do this.

I’m making a swing Java app with multi-threading.
I have many swing component (textfield, texarea, label, list, …) which are set and refresh with many threads.

For all my component I use something like the code below (it’s just a tiny example) for set/refresh it.

Is Main.mainUI.setThumbLbl(image); for set/refresh my component a good way or not ? (I use something like this in other threads for all component)
And is there another better way to do this ?

Main :

public class Main {

  public static MyMainUI mainUI;

  public static void main(String args[]) {
    mainUI = new mainUI();
    java.awt.EventQueue.invokeLater(new Runnable() {

      @Override
      public void run() {        
        mainUI.setVisible(true);
      }
    });
  }
}

Jframe :

public class MyMainUI extends JFrame {

  private JLabel thumbLbl;
  private JButton thumbBtn;

  public MyMainUI(){
    // add thumbLbl, thumBtn
    ...
    thumBtn.addMouseListener(new MouseAdapter() {
      @Override
      public void mouseReleased(MouseEvent evt) {
        new MyThread().start();
      }
    });
  }

  public void setThumbLbl(final Image image) {
    SwingUtilities.invokeLater(new Thread() {

      @Override
      public void run() {
        thumbLbl.setIcon(new ImageIcon(image.getScaledInstance(thumbLblDim.width,
           thumbLblDim.height, Image.SCALE_DEFAULT)));
      }
    });
  }
}

Thread :

public class MyThread extends Thread {
  @Override
  public void run() {
    //Get image from web server
    ...
    Main.mainUI.setThumbLbl(image);
  }
}

NB: I wrote this sample code in a text editor very quickly, maybe there are some mistakes but it’s not what I’m asking for ^^.
NB2: Sorry for my bad English.

Answer 1

An example of what I meant is something like this:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.concurrent.ExecutionException;

import javax.imageio.ImageIO;
import javax.swing.*;

public class Main {
   private static void createAndShowGui() {
      JFrame frame = new JFrame("Main");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new MyMainUI());
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
 }

@SuppressWarnings("serial")
class MyMainUI extends JPanel {
   public static final String IMG_URL_PATH = "http://duke.kenai.com/Oracle/OracleStrat.png";
   private static final int PREF_W = 900;
   private static final int PREF_H = 650; 
   private JLabel thumbLbl = new JLabel();
   private JButton thumbBtn = new JButton("Get Image");

   public MyMainUI() {      
      thumbBtn.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent arg0) {
            thumbBtn.setEnabled(false);
            final ImageDownloader imgDownLoader = new ImageDownloader(IMG_URL_PATH);
            imgDownLoader.execute();

            imgDownLoader.addPropertyChangeListener(new ImgDownLoaderListener(imgDownLoader));
         }
      });

      JPanel btnPanel = new JPanel();
      btnPanel.add(thumbBtn);

      setLayout(new BorderLayout());
      add(new JScrollPane(thumbLbl), BorderLayout.CENTER);
      add(btnPanel, BorderLayout.PAGE_END);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private class ImgDownLoaderListener implements PropertyChangeListener {
      ImageDownloader imgDownLoader;

      public ImgDownLoaderListener(ImageDownloader imgDownLoader) {
         this.imgDownLoader = imgDownLoader;
      }

      @Override
      public void propertyChange(PropertyChangeEvent evt) {
         // swing worker is done
         if (evt.getNewValue().equals(SwingWorker.StateValue.DONE)) {
            thumbBtn.setEnabled(true);
            try {
               ImageIcon icon = imgDownLoader.get();
               if (icon != null) {
                  thumbLbl.setIcon(icon);
               }
            } catch (InterruptedException e) {
               e.printStackTrace();
            } catch (ExecutionException e) {
               e.printStackTrace();
            }
         }
      }
   }
}



class ImageDownloader extends SwingWorker<ImageIcon, Void> {
   private String imageUrlPath;

   public ImageDownloader(String imageUrlPath) {
      this.imageUrlPath = imageUrlPath;
   }

   @Override
   protected ImageIcon doInBackground() throws Exception {
      try {
         URL imgUrl = new URL(imageUrlPath);
         BufferedImage img = ImageIO.read(imgUrl);
         return new ImageIcon(img); // return the ImageIcon
      } catch (MalformedURLException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
      return null; // or return null if an error occurs
   }

}

The background worker thread in this example has no knowledge about the structure of the GUI. All it does is download an image — that’s it, and then the GUI which listens for completion with a PropertyChangeListener gets the image by calling get() on the worker, and decides what it wants to do with it.