Annoying program, please help

Question

I wrote an JFrame draw program which can work well by itself class D. However, when I call it from the other class B using B's JFrame, the drawing can't display. What happens?
import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
import javax.swing.*;
public class D extends JApplet{
    public void init() {
    public void paint(Graphics g) {
  Graphics2D g2=(Graphics2D)g;
     g2.draw(new Line2D.Double(0,0,100,100));
/*public static void main(String[] args){
        JFrame f = new JFrame("2D draw");
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {System.exit(0);}
        JApplet applet = new D();
        f.getContentPane().add("Center", applet);
        applet.init();
        f.pack();
        f.setSize(new Dimension(500,500));
        f.show();
When I use in B class:
JFrame f=new JFrame();
Container content=f.getContentPane();
JButton button4=new JButton("Test");
     ActionListener b4_al=new ActionListener(){
             public void actionPerformed(ActionEvent ae){
                try{
                JApplet applet = new D();
               content.add("Center", applet);
               applet.init();
               f.pack();
               f.setSize(new Dimension(500,500));
               f.show(true);
       }catch (Exception e){}
        button4.addActionListener(b4_al);

Answer 1

Worked for me.
Some few changes I made (had to make the frame final,
add the button to the frame, size and show the frame).
(sorry 'bout name of MouseMoveTest, just use it as my general test file now...)
import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
import javax.swing.*;
public class MouseMoveTest {
  public static void main (String[] args) {
       final JFrame f=new JFrame();
       final Container content=f.getContentPane();
       JButton button4=new JButton("Test");
       ActionListener b4_al=new ActionListener(){
            public void actionPerformed(ActionEvent ae){
                 try{
                      JApplet applet = new D();
                      content.add("Center", applet);
                      applet.init();
                      f.pack();
                      f.setSize(new Dimension(500,500));
                      f.show(true);
                 }catch (Exception e){}
       button4.addActionListener(b4_al);
       content.add(button4);
       f.setSize(new Dimension(500,500));
       f.show(true);
class D extends JApplet {
     public void init() {
     public void paint(Graphics g) {
          Graphics2D g2=(Graphics2D)g;
          g2.draw(new Line2D.Double(0,0,100,100));
}