My code compiles and runs but the GUI will not display. I have tinkered with it but cannot get it to come up. Someone said I may be miscalling my GUI in this code, help?

Thank you.

Code:
import javax.swing.*;

import java.awt.event.*;

public class Application_MainRunInv extends JFrame {

private JTextArea txt;
private Inventory inv;
private int currentDisplay = 0;
...