Add first in linkedlist

 I/P:

addFirst 10 getFirst addFirst 20 getFirst getLast display size addLast 40 getLast addLast 50 addFirst 30 removeFirst getFirst removeFirst removeFirst getAt 3 display size removeFirst removeFirst getFirst quit

O/P:

10 20 10 20 10 2 40 20 Invalid arguments 40 50 2 List is empty

package pep.Day13;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Add_First_In_LinkedList {
    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;
            }
        }

        // write your code here
        public void addFirst(int val) {
            Node temp = new Node();
            temp.data = val;
            temp.next = null;
            if (size == 0) {
                head = temp;
                tail=temp;
            } else {
                temp.next = head;
                head = temp;

            }
            size++;
        }
    }

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

        String str = br.readLine();
        while (str.equals("quit") == false) {
            if (str.startsWith("addLast")) {
                int val = Integer.parseInt(str.split(" ")[1]);
                list.addLast(val);
            } else if (str.startsWith("size")) {
                System.out.println(list.size());
            } else if (str.startsWith("display")) {
                list.display();
            } else if (str.startsWith("removeFirst")) {
                list.removeFirst();
            } else if (str.startsWith("getFirst")) {
                int val = list.getFirst();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("getLast")) {
                int val = list.getLast();
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("getAt")) {
                int idx = Integer.parseInt(str.split(" ")[1]);
                int val = list.getAt(idx);
                if (val != -1) {
                    System.out.println(val);
                }
            } else if (str.startsWith("addFirst")) {
                int val = Integer.parseInt(str.split(" ")[1]);
                list.addFirst(val);
            }
            str = br.readLine();
        }
    }
}