Merge Two Sorted Linked Lists

I/O:

5 10 20 30 40 50 10 

7 9 12 15 37 43 44 48 52 56

O/P:

7 9 10 12 15 20 30 37 40 43 44 48 50 52 56 10 20 30 40 50  

7 9 12 15 37 43 44 48 52 56  

package pep.Day15;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.LinkedList;

public class Merge_Two_Sorted_LinkedLists {
    public static class Node {
        int data;
        Node next;
    }

    public static class LinkedList {
        Node head;
        Node tail;
        int size;

        void addLast(int val) {
            Node temp = new Node();
            temp.data = val;
            temp.next = null;

            if (size == 0) {
                head = tail = temp;
            } else {
                tail.next = temp;
                tail = temp;
            }

            size++;
        }

        public int size() {
            return size;
        }

        public void display() {
            for (Node temp = head; temp != null; temp = temp.next) {
                System.out.print(temp.data + " ");
            }
            System.out.println();
        }

        public void removeFirst() {
            if (size == 0) {
                System.out.println("List is empty");
            } else if (size == 1) {
                head = tail = null;
                size = 0;
            } else {
                head = head.next;
                size--;
            }
        }

        public int getFirst() {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else {
                return head.data;
            }
        }

        public int getLast() {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else {
                return tail.data;
            }
        }

        public int getAt(int idx) {
            if (size == 0) {
                System.out.println("List is empty");
                return -1;
            } else if (idx < 0 || idx >= size) {
                System.out.println("Invalid arguments");
                return -1;
            } else {
                Node temp = head;
                for (int i = 0; i < idx; i++) {
                    temp = temp.next;
                }
                return temp.data;
            }
        }

        public void addFirst(int val) {
            Node temp = new Node();
            temp.data = val;
            temp.next = head;
            head = temp;

            if (size == 0) {
                tail = temp;
            }

            size++;
        }

        public void addAt(int idx, int val) {
            if (idx < 0 || idx > size) {
                System.out.println("Invalid arguments");
            } else if (idx == 0) {
                addFirst(val);
            } else if (idx == size) {
                addLast(val);
            } else {
                Node node = new Node();
                node.data = val;

                Node temp = head;
                for (int i = 0; i < idx - 1; i++) {
                    temp = temp.next;
                }
                node.next = temp.next;

                temp.next = node;
                size++;
            }
        }

        public int mid() {
            Node f = head;
            Node s = head;

            while (f.next != null && f.next.next != null) {
                f = f.next.next;
                s = s.next;
            }

            return s.data;
        }

        // write your code here
        public static LinkedList mergeTwoSortedLists(LinkedList l1, LinkedList l2) {
            LinkedList ll = new LinkedList();
            Node p1 = l1.head, p2 = l2.head;

            while (p1 != null && p2 != null) {
                if (p1.data < p2.data) {
                    ll.addLast(p1.data);
                    p1 = p1.next;
                } else {
                    ll.addLast(p2.data);
                    p2 = p2.next;
                }
            }

            while (p1 != null) {
                ll.addLast(p1.data);
                p1 = p1.next;
            }

            while (p2 != null) {
                ll.addLast(p2.data);
                p2 = p2.next;
            }

            return ll;
        }
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int n1 = Integer.parseInt(br.readLine());
        LinkedList l1 = new LinkedList();
        String[] values1 = br.readLine().split(" ");
        for (int i = 0; i < n1; i++) {
            int d = Integer.parseInt(values1[i]);
            l1.addLast(d);
        }

        int n2 = Integer.parseInt(br.readLine());
        LinkedList l2 = new LinkedList();
        String[] values2 = br.readLine().split(" ");
        for (int i = 0; i < n2; i++) {
            int d = Integer.parseInt(values2[i]);
            l2.addLast(d);
        }

        LinkedList merged = LinkedList.mergeTwoSortedLists(l1, l2);
        merged.display();
        l1.display();
        l2.display();
    }
}