Add a node at the end of a Singly Linked List

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/*Node of a single linked list of integer */
public class SinglyLinkedList {
	private static Node head; /* instance variable */

	private static class Node {
		private int data; /* we assume data integer */
		private Node next; /* Create a node with the given data and next node */

		public Node(int data) {
			this.data = data;
			this.next = null;
		}
	}
	
	/* Display the single linked list */
	public void display() {
		Node current = head;
		while (current != null) {
			System.out.print(current.data + " --> ");
			current = current.next;
		}
		System.out.println("null");
	}
	//Add a node at the end of a Singly Linked List
	public void insertEnd(int value) {
		Node newNode = new Node(value);
		if(head==null) {
			head = newNode;
			return;
		}
		Node current = head;
		while(current.next!=null) {
			current = current.next;
		}
		current.next = newNode;
	}

	public static void main(String[] args) {
		SinglyLinkedList s = new SinglyLinkedList();
		s.head = new Node(10);
		Node second = new Node(7);
		Node third = new Node(20);
		Node fourth = new Node(8);

		s.head.next = second; // 10 --> 7
		second.next = third; // 10 -->7 -->20
		third.next = fourth; // 10 -->7 --> 20 -->8 -->null
		System.out.println("Before Insert:");
		s.display();
		
		System.out.println("After Insert:");
		s.insertEnd(15); // 10 -->7 --> 20 -->8 -->15 -->null
		s.display();
	}

}