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Java program to insert a new node at the beginning of the singly linked list

public class InsertStart {

//Represent a node of the singly linked list
class Node{
int data;
Node next;

public Node(int data) {
this.data = data;
this.next = null;
}
}

//Represent the head and tail of the singly linked list
public Node head = null;
public Node tail = null;

//addAtStart() will add a new node to the beginning of the list
public void addAtStart(int data) {
//Create a new node
Node newNode = new Node(data);

//Checks if the list is empty
if(head == null) {
//If list is empty, both head and tail will point to new node
head = newNode;
tail = newNode;
}
else {
//Node temp will point to head
Node temp = head;
//newNode will become new head of the list
head = newNode;
//Node temp(previous head) will be added after new head
head.next = temp;
}
}

//display() will display all the nodes present in the list
public void display() {
//Node current will point to head
Node current = head;
if(head == null) {
System.out.println("List is empty");
return;
}
System.out.println("Adding nodes to the start of the list: ");
while(current != null) {
//Prints each node by incrementing pointer
System.out.print(current.data + " ");
current = current.next;
}
System.out.println();
}

public static void main(String[] args) {

InsertStart sList = new InsertStart();

//Adding 1 to the list
sList.addAtStart(1);
sList.display();

//Adding 2 to the list
sList.addAtStart(2);
sList.display();

//Adding 3 to the list
sList.addAtStart(3);
sList.display();

//Adding 4 to the list
sList.addAtStart(4);
sList.display();
}
}

Output:
Adding nodes to the start of the list:
1
Adding nodes to the start of the list:
2 1
Adding nodes to the start of the list:
3 2 1
Adding nodes to the start of the list:
4 3 2 1

Adding nodes to the start of the list:
1
Adding nodes to the start of the list:
2 1
Adding nodes to the start of the list:
3 2 1
Adding nodes to the start of the list:
4 3 2 1

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