repaint() fails to work

Question

I wanted to draw an image on my panel based on the data I receive from another thread. I am sure the data and consequent pixel array works well, but the repaint() would never work. Can anyone tell me what's going wrong here?

import javax.swing.*;
import java.awt.*;
import java.awt.image.*;

/** Create an image from a pixel array. **/
public class PicturePlaza extends JApplet
{
  ImagePanel fImagePanel;
  ReadCom   readComPort;
  Thread readPortThread;

  public void init () {
    // initiate the read port thread so that it can receive data
     readComPort = new ReadCom();
     readPortThread = new Thread(readComPort,"ReadCom");
     readPortThread.start();

     Container content_pane = getContentPane ();
     fImagePanel = new ImagePanel ();
     content_pane.add (fImagePanel);  

  } 

  // Tell the panel to create and display the image, if pixel data is ready.
  public void start () {
      while(true){
          if(readComPort.newPic){
              fImagePanel.go();
          }
          try {
                    Thread.sleep(4000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
      }
  }


/** Create an image from a pixel array. **/
  class ImagePanel extends JPanel{
      Image fImage;
      int fWidth = ReadCom.row, fHeight = ReadCom.col;      

      void go() {         
                    //update the image if newPic flag is set to true                
                    fImage = createImage (new MemoryImageSource (fWidth, fHeight, ReadCom.fpixel, 0, fWidth));
                    repaint();
                    readComPort.newPic = false; //disable the flag, indicating the image pixel has been used                                                            
      } 

      /** Paint the image on the panel. **/
      public void paintComponent (Graphics g) {
        super.paintComponent (g);       
        g.drawImage (fImage, 0, 0, this );  
      } 
  } 
}

Thanks

Answer 1

Just a little note on repaint(). repaint() schedules a repaint of the screen, it won't always do it immediately in my experience. I found the best solution is to directly call paint() yourself.

Graphics g;
g = getGraphics();
paint(g);

I put this as a new function to call in my code when I wanted it to paint immediately. Also this will not erase the previous graphics on the screen, you will have to do that manually.