How can I run an applet as an application?

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Java

Dears,
I have an Applet class, and I want to make it run as an application, so I wrote to following code:

public static void main(String args[]) {
JFrame app = new JFrame("Applet Container");
app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
app.setSize(200, 100);
Hangman applet = new Hangman();
applet.init();
app.setLayout(new BorderLayout());
app.setSize(500,500);
app.getContentPane().add(applet, BorderLayout.CENTER);
app.setVisible(true);
}

Note: Hangman is the applet class. And if i run it, it work fine, but what I am tring to do, is to make it run as an application.
When I run the above main, I got the following error:

Exception in thread "main" java.lang.NullPointerException
at java.applet.Applet.getCodeBase(Applet.java:152)
at Me.Hangman.init(Hangman.java:138)
at Me.Client.main(Client.java:54)
Java Result: 1

This error is came from this line in the Hangman class:

danceMusic = getAudioClip(getCodeBase(), "../../audio/dance.au");

GetCodeBase() method returns null, I need help on how can I make this method work properly, or maybe replace it with another method that may access my files to get resources?
Thank you in advance