1.0

//a linked list node
public class Node {
    int data;
    Node next;
    Node(int data, Node next){
        this.data=data;
        this.next=next;
    }
}
class Main {
    // helper function to return new linked list node from heap
    public static Node newNode(int key) {
        Node node = new Node(key, null);
        return node;
    }

    // helper function to print linked list
    public static void printList(Node head) {
        Node ptr = head;
        while (ptr != null) {
            System.out.print(ptr.data + " -> ");
            ptr = ptr.next;

        }
        System.out.println("null");
    }
// function to add a new node at the tail end of the list instead of its head
    public static Node appendNode(Node head , int key){
        Node current = head;
        Node node = newNode(key);
        //special case for length 0
        if(current == null){
         head = node;
        }
        else {
            while (current.next!=null){
                current=current.next;

            }
            current.next=node;
        }
        return head;

    }
    //main method to implement linked list
    public static void main (String [] args){
        //input keys
        int [] keys = {1 , 2 , 3 , 4 };
        // points to the head node of the linked list
        Node head = null;
        for(int key : keys){
            head = appendNode(head , key);
        }
        //print linked list
        printList(head);
    }
}