The basic window in Swing

import javax.swing.*;

public class HelloFrame extends __________{

    public HelloFrame() {
        super("My First Swing App");
        setSize(300, 300);
        setLocationRelativeTo(null);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }

    public static void main(final String[] args) {
        new HelloFrame();
    }
}

Which of the following class can be used for space in the above code?