Exporting Project In Eclipse?

i have programmed a game using JPanel and JFrame. My App is of this type (if this is relevant to the problem):

public class Main extends JPanel {
 private JFrame frame;
public static void main(String[] args) {
new Main();
} public Main() {
frame.setSize(WIDTH, HEIGHT);

[Code] ....

The problem is, When i export the file in eclipse as Runnable jar file,and run the exported file, it gives me a blank screen (white default) and nothing is running. Whereas, normal debugging of the game is working quite well.