Linked List creation, Java

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//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_111

import java.util.*;
import java.lang.*;
class Node{
    int data;
    Node next;
    Node(int data){
        this.data = data;
        this.next=null;
    }
}
class Rextester
{  
    Node head=null;
    public void  insertFirst(int data){
        if(head==null){
            Node n = new Node(data);
            head = n;
            return;
        }
        else{
            Node n = new Node(data);
            n.next = head;
            head = n;
            return;
    }
    }
    public void insertLast(int data){
        if(head==null){
            Node n = new Node(data);
            head = n;
            return;
        }
        else{
            Node n = new Node(data);
            Node pre = head;
            while(pre.next!=null){
                pre = pre.next;
            }
            pre.next = n;
        }
    }
    public void insert(int data,int pos){
        Node ne  = head;
        int count=0;
        while(count<pos-1){
            count++;
            ne = ne.next;
        }
        Node n = new Node(data);
        n.next = ne.next;
        ne.next = n;
    }
    public void display(){
        Node n = head;
        while(n!=null){
            System.out.println(n.data);
            n = n.next;
        }
    }
    public void deleteFirst(){
        if(head==null){
            System.out.println("Empty lIst");
        }
        else{
            Node n = head;
            head = n.next;
        }
    }
    public void deleteLast(){
        if(head==null){
            System.out.println("Empty list");
        }
        else{
            Node n = head;
            Node pre = null;
            while(n.next!=null){
                pre = n;
                n = n.next;
           }
           pre.next = null;
    }
    }
        public void delete(int pos){
            Node n = head;
            Node pre = null;
            int count=0;
            while(count!=pos-1){
                count++;
                pre = n;
                n = n.next;
            }
            pre.next = n.next;
        }
    
    public static void main(String args[])
    {
        Rextester r = new Rextester();
        r.insertFirst(1);
        r.insertLast(10);
        r.insert(2,2);
        r.insertLast(20);
        
        r.deleteFirst();
        r.deleteLast();
        r.delete(2);
        r.display();
    }
}

[ + ] Show input
Compilation time: 1.04 sec, absolute running time: 0.17 sec, cpu time: 0.15 sec, memory peak: 18 Mb, absolute service time: 1,23 sec