Java Program For Inserting A Node In A Linked List

// Linked List Class
class LinkedList
{
    // Head of list
    Node head;  

    // Node Class 
    class Node
    {
        int data;
        Node next;
         
        // Constructor to create
        // a new node
        Node(int d) 
        {
            data = d; 
            next = null; 
        }
    }
}

/* This function is in LinkedList class. Inserts a
   new Node at front of the list. This method is 
   defined inside LinkedList class shown above */
public void push(int new_data)
{
    /* 1 & 2: Allocate the Node &
              Put in the data*/
    Node new_node = new Node(new_data);

    // 3. Make next of new Node as head 
    new_node.next = head;

    // 4. Move the head to point to 
    // new Node 
    head = new_node;
}

/* This function is in LinkedList class. 
   Inserts a new node after the given 
   prev_node. This method is defined 
   inside LinkedList class shown above */
public void insertAfter(Node prev_node, 
                        int new_data) 
{ 
    // 1. Check if the given Node is null 
    if (prev_node == null) 
    { 
        System.out.println(
               "The given previous node cannot be null"); 
        return; 
    } 

    /* 2. Allocate the Node & 
       3. Put in the data*/
    Node new_node = new Node(new_data); 

    // 4. Make next of new Node as next
    // of prev_node 
    new_node.next = prev_node.next; 

    // 5. make next of prev_node as new_node 
    prev_node.next = new_node; 
} 

/* Appends a new node at the end.  This method is 
   defined inside LinkedList class shown above */
public void append(int new_data)
{
    /* 1. Allocate the Node &
       2. Put in the data
       3. Set next as null */
    Node new_node = new Node(new_data);

    /* 4. If the Linked List is empty, then 
          make the new node as head */
    if (head == null)
    {
        head = new Node(new_data);
        return;
    }

    /* 4. This new node is going to be the 
          last node, so make next of it 
          as null */
    new_node.next = null;

    // 5. Else traverse till the last node 
    Node last = head; 
    while (last.next != null)
        last = last.next;

    // 6. Change the next of last node 
    last.next = new_node;
    return;
}

// A complete working Java program to 
// demonstrate all insertion methods
// on linked list
class LinkedList
{
    // head of list
    Node head;  

    // Linked list Node
    class Node
    {
        int data;
        Node next;
        Node(int d) 
        {
            data = d; 
            next = null; 
        }
    }

    // Inserts a new Node at front 
    // of the list. 
    public void push(int new_data)
    {
        /* 1 & 2: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);

        // 3. Make next of new Node as head 
        new_node.next = head;

        // 4. Move the head to point to
        // new Node 
        head = new_node;
    }

    // Inserts a new node after the 
    // given prev_node. 
    public void insertAfter(Node prev_node, 
                            int new_data)
    {
        // 1. Check if the given Node is null 
        if (prev_node == null)
        {
            System.out.println(
                   "The given previous node cannot be null");
            return;
        }

        /* 2 & 3: Allocate the Node &
                  Put in the data*/
        Node new_node = new Node(new_data);

        // 4. Make next of new Node as next 
        // of prev_node 
        new_node.next = prev_node.next;

        // 5. make next of prev_node as 
        // new_node 
        prev_node.next = new_node;
    }
   
    /* Appends a new node at the end. 
       This method is defined inside 
       LinkedList class shown above */
    public void append(int new_data)
    {
        /* 1. Allocate the Node &
           2. Put in the data
           3. Set next as null */
        Node new_node = new Node(new_data);

        /* 4. If the Linked List is empty, 
              then make the new node as head */
        if (head == null)
        {
            head = new Node(new_data);
            return;
        }

        /* 4. This new node is going to be 
              the last node, so make next 
              of it as null */
        new_node.next = null;

        // 5. Else traverse till the last node 
        Node last = head; 
        while (last.next != null)
            last = last.next;

        // 6. Change the next of last node 
        last.next = new_node;
        return;
    }

    /* This function prints contents of 
       linked list starting from the 
       given node */
    public void printList()
    {
        Node tnode = head;
        while (tnode != null)
        {
            System.out.print(tnode.data + " ");
            tnode = tnode.next;
        }
    }

    // Driver code
    public static void main(String[] args)
    {
        // Start with the empty list 
        LinkedList llist = new LinkedList();

        // Insert 6. So linked list 
        // becomes 6->NUllist
        llist.append(6);

        // Insert 7 at the beginning. 
        // So linked list becomes 
        // 7->6->NUllist
        llist.push(7);

        // Insert 1 at the beginning. 
        // So linked list becomes
        // 1->7->6->NUllist
        llist.push(1);

        // Insert 4 at the end. 
        // So linked list becomes
        // 1->7->6->4->NUllist
        llist.append(4);

        // Insert 8, after 7. So linked 
        // list becomes
        // 1->7->8->6->4->NUllist
        llist.insertAfter(llist.head.next, 8);

        System.out.println(
               "Created Linked list is: ");
        llist.printList();
    }
}
// This code is contributed by Rajat Mishra