JFrame을 실행하는 동안 null 포인트 예외가 발생합니다.

import java.awt.*;
import javax.swing.*;




class Performance{

private JLabel l1;

private JLabel l2;

  private JLabel l3;

  private JLabel l4;

  private JLabel l5;

  private JLabel l6;

  private JLabel l7;

  private JLabel l8;

  private JLabel l9;

  private JComboBox c1;

  private JComboBox c2;

  private JComboBox c3;

  private JComboBox c4;

  private JComboBox c5;

  private JComboBox c6;

  private JComboBox c7;

  private JComboBox c8;

  private JComboBox c9;

  private String s1[] ={"S","A","B","C","D","E","U"};

  private String s2[] ={"S","A","B","C","D","E","U"};

  private String s3[] ={"S","A","B","C","D","E","U"};

  private String s4[] ={"S","A","B","C","D","E","U"};

  private String s5[] ={"S","A","B","C","D","E","U"};

  private String s6[] ={"S","A","B","C","D","E","U"};

  private String s7[] ={"S","A","B","C","D","E","U"};

  private String s8[] ={"S","A","B","C","D","E","U"};

  private String s9[] ={"S","A","B","C","D","E","U"};

  private JButton submit;

  private JFrame f;

    public void Performance(){
        f = new JFrame("CGPA calc for cse sem6");
        l1 = new JLabel("AI");
        l2 = new JLabel("PCD");
        l3 = new JLabel("OOAD");
        l4 = new JLabel("ACA");
        l5 = new JLabel("WT");
        l6 = new JLabel("KM");
        l7 = new JLabel("LAB1");
        l8 = new JLabel("LAB2");
        l9 = new JLabel("LAB3");
        c1 = new JComboBox(s1);
        c2 = new JComboBox(s2);
        c3 = new JComboBox(s3);
        c4 = new JComboBox(s4);
        c5 = new JComboBox(s5);
        c6 = new JComboBox(s6);
        c7 = new JComboBox(s7);
        c8 = new JComboBox(s8);
        c9 = new JComboBox(s9);
                submit = new JButton("Submit");
    }

    public void Lancher(){
        f.setLayout(new GridLayout(10,2,10,10));
        f.setVisible(true);
        f.setSize(300,300);
        f.add(l1);
        f.add(c1);
        f.add(l2);
        f.add(c2);
        f.add(l3);
        f.add(c3);
        f.add(l4);
        f.add(c4);
        f.add(l5);
        f.add(c5);
        f.add(l6);
        f.add(c6);
        f.add(l7);
        f.add(c7);
        f.add(l8);
        f.add(c8);
        f.add(l9);
                f.add(c9);
                f.add(submit);
    }
}

public class cse_sem6
{

public static void main(String a[]){

  Performance obj = new Performance();

  obj.Lancher();

}
}