Linked List print

package kel6;                                           //Ihsan, April, Fazar, Vini
import java.util.*;
import javax.swing.*;
import static javax.swing.JOptionPane.showInputDialog;
public class kelompok6_tugas2 {
    int data;
    kelompok6_tugas2 next;


    kelompok6_tugas2()
    {
        data = 0;
        next = null;
    }


        public void tambah_depan (kelompok6_tugas2 h, int data){  //method tambah depan
            kelompok6_tugas2 p = new kelompok6_tugas2();
            p = h;
            kelompok6_tugas2 q = new kelompok6_tugas2();
            q.data = data;
            q.next = p.next;
            p.next = q;

}

       public void tambah_belakang (kelompok6_tugas2 h, int data){ //method tambah belakang
           kelompok6_tugas2 p = new kelompok6_tugas2();
           kelompok6_tugas2 q = new kelompok6_tugas2();
           q.data = data;
           q.next = null;
           p = h;
           while (p.next!=null)
               p = p.next;
           p.next = q;

       }

       public void hapus_belakang(kelompok6_tugas2 h){ //method hapus belakang
           kelompok6_tugas2 p = new kelompok6_tugas2();
           p = h;
           if (p.next!=null){
               while (p.next.next!=null)
                   p = p.next;
               p.next = null;
           }
           else
               JOptionPane.showMessageDialog(null, "Linked list kosong");
       }

       public void hapus_depan(kelompok6_tugas2 h){ //method hapus depan
           kelompok6_tugas2 p = new kelompok6_tugas2();
           p = h;
           if(p.next!=null){
               p.next = p.next.next;
           }
           else
               JOptionPane.showMessageDialog(null, "Linked list kosong");
           }

       public void tampil_list(kelompok6_tugas2 h){ //method menampilkan data
           kelompok6_tugas2 current = h;
           String output = " ";
           while (current != null)
           {
               output += current.data + "\n";
               current = current.next;
           }
           JOptionPane.showMessageDialog(null, output + "\n\n DATA Ditampilkan!");
       }



    public static void main(String[] args) {
        kelompok6_tugas2 head = new kelompok6_tugas2();
        head.next = null;

          int choice, data;

        kelompok6_tugas2 list = new kelompok6_tugas2();

        do
        {
            String menu = "1. Tambah data (depan)\n2. Tambah data (Belakang)\n3. Hapus data (depan)\n4. Hapus data (Belakang)\n5. Tampilkan\n6. Exit.";

            choice = Integer.parseInt(showInputDialog(menu + "\nMasukan angka"));

            switch (choice)
            {
                case 1:
                data = Integer.parseInt(showInputDialog("Masukan data:"));
                list.tambah_depan(head, data);
                break;

                case 2:
                data = Integer.parseInt(showInputDialog("Masukan data:"));
                list.tambah_belakang(head, data);
                break;

                case 3:
                list.hapus_depan(head);
                break;

                case 4:
                list.hapus_belakang(head);

                case 5:
                list.tampil_list(head);
                break;

                case 6:
                break;
            }
        } while (choice != 6);
    }
}