public class MyApplet extends JApplet {
	public void init() {
		super.init();
		JButton btnLaunch = new JButton("Launch");
		btnLaunch.addActionListener(new ActionListener() {
			@Override public void actionPerformed(ActionEvent e) {
				new FakeMainWindow(getParameter("server"));
			}
		});
		getContentPane().add(btnLaunch);
	}
}

---

public class FakeMainWindow extends JFrame {
	private static final long serialVersionUID = -2398748084588857421L;

	public FakeMainWindow(String x) {
		super("test: " + x);
		setVisible(true);
	}
}