It would help if you could post the part of your code where you initialize your PApplet and add it to the JFrame. After initializing, init() has to be invoked to begin running it.

You might need a pack() call on the JFrame too.

Hi manindra29 and All,

     My PApplet and JFrame programs are listed below :

----------
package mytest.papplet_in_java_frame;

import processing.core.*;

public class Embedded_Demo extends PApplet {
    public boolean ok = false;

    public void setup() {
        size(500, 500, P2D);
        drawImpl();
        // Indicator to external program to show that the drawing process has finished.
        ok = true;
        noLoop();
    }
    public void draw() {
        drawImpl();
    }
    public void drawImpl()  {
        stroke(50);
        fill(0,0,255);
        translate(0, 0);
        rect(0,0,30,30);
    }
    public void mousePressed() {
        loop();
    }
    public void mouseReleased() {
        noLoop();
    }
}
----------
package mytest.papplet_in_java_frame;

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

public class ExampleJFrame_Demo extends JFrame {
    Embedded_Demo embed;

    public ExampleJFrame_Demo() {
        super("Embedded PApplet");
        setLayout(new BorderLayout());
        embed = new Embedded_Demo();
        embed.init();
       
        // *** Because PApplet runs with its own thread, so here we must
        //        wait for its thread to finish processing its graphics.
        while (embed.ok == false )  {
            System.out.println("PApplet is not ready !");
        }
        System.out.println("It's now ready");
       
        // The embedded PApplet should be added to the JFrame after it is
        //   fully initialized.
        add(embed, BorderLayout.CENTER);
    }
    public static void main(String[] args) throws Exception {
        ExampleJFrame_Demo myFrame = new ExampleJFrame_Demo();
        myFrame.setResizable(true);
        myFrame.setSize(500,500);
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        myFrame.setVisible(true);
    }
}
----------

     I am sorry that I have made a mistake in my previous post. As I have defined the "mousePressed()" method with the "loop()" command in the "Embedded_Demo" class, so I have actually drawn my picture when I make a mouse click ! (There may be nothing to concern with Java GUI painting)

     However, what I really wonder is that if I delete the "mousePressed()" and "mouseReleased()" method in the "Embedded_Demo" class, I could NOT see any picture (only a blank picture) in the drawing area of the PApplet, even when I make mouse clicks on it. I suppose that I have drawn the picture once in the "setup()" method of the "Embedded_Demo" class, but that picture is lost (or not being displayed / refreshed) when the PApplet is added (embedded) into a JFrame.

     In the "ExampleJFrame_Demo" class, I have inserted codes to init the PApplet and wait for it to be ready. But I could still not able to display the statically drawn picture in the PApplet.

     Is there any way that I could temporarily by-pass the PApplet's "draw" method and just use its "setup" method to draw a static picture that could be embedded and displayed in a JFrame ? Or is there a good approach that I could use PApplet to draw a static picture and display it in a JFrame ?

     Thanks for your suggestions.

Regards
Lawrence

Random suggestion: put the drawing code in draw(), and add the noLoop() at the end of draw().

So, I tested your code, with some minor changes to check (only one file, to simplify).
For the record, I compiled it with the command javac -cp core.jar ExampleJFrame_Demo.java and ran it with java -cp .;core.jar ExampleJFrame_Demo
(on Windows 7, with Java 1.6.0_25
Each time I ran it, I saw the Processing applet, no problem like those you describe. Perhaps you have an issue with your configuration.

1. import java.awt.*;
2. import javax.swing.JFrame;
3. import processing.core.*;
4. 
   
5. class Embedded_Demo extends PApplet {
6.     public boolean ok;
7.     public void setup() {
8.         size(500, 500, P2D);
9.         drawImpl();
10.         // Indicator to external program to show that the drawing process has finished.
11.         ok = true;
12.         noLoop();
13.     }
14. 
    
15.     public void drawImpl()  {
16.         stroke(50);
17.         fill(0,0,255);
18.         for (int i = 0; i < 10; i++) {
19.             translate(20, 20);
20.             rect(0,0,30,30);
21.         }
22.     }
23. }
24. 
    
25. public class ExampleJFrame_Demo extends JFrame {
26.     Embedded_Demo embed;
27. 
    
28.     public ExampleJFrame_Demo() {
29.         super("Embedded PApplet");
30.         setLayout(new BorderLayout());
31.         embed = new Embedded_Demo();
32.         embed.init();
33.         add(embed, BorderLayout.CENTER);
34.     }
35. 
    
36.     public static void main(String[] args) throws Exception {
37.         ExampleJFrame_Demo myFrame = new ExampleJFrame_Demo();
38.         myFrame.setResizable(true);
39.         myFrame.setSize(500,500);
40.         myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
41.         myFrame.pack();
42.         myFrame.setVisible(true);
43.     }
44.  
45. // Canonical Swing should be started this way, in its own thread.
    
46. //~     public static void main(String[] args) throws Exception {
47. //~         javax.swing.SwingUtilities.invokeLater(new Runnable()
48. //~         {
49. //~             public void run()
50. //~             {
51. //~                 ExampleJFrame_Demo myFrame = new ExampleJFrame_Demo();
52. //~                 myFrame.setResizable(true);
53. //~                 myFrame.setSize(500, 500);
54. //~                 myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
55. //~                 myFrame.pack();
56. //~                 myFrame.setVisible(true);
57. //~             }
58. //~         });
59. //~     }
60. }