Java program to create a doubly linked list of n nodes and count the number of nodes

by Online Tutorials Library July 22, 2022

Java program to create a doubly linked list of n nodes and count the number of nodes

In this program, we will create a doubly linked list and count the number of nodes present in the list. To count the node, we traverse through the list by incrementing the counter by 1.

What count of nodes presents above doubly linked list is 5.

Algorithm

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
addNode() will add node to the list:
- It first checks whether the head is null, then it will insert the node as the head.
- Both head and tail will point to a newly added node.
- Head’s previous pointer will point to null and tail?s next pointer will point to null.
- If the head is not null, the new node will be inserted at the end of the list such that new node’s previous pointer will point to tail.
- The new node will become the new tail. Tail’s next pointer will point to null.

a. countNodes() will count the number of nodes present in the list.

Define a variable counter and new node current which will point to the head node.
Traverse through the list to count the nodes by making the current node to point to next node in the list till current point to null.
Increment the counter by 1.

a. display() will show all the nodes present in the list.

Define a new node ‘current’ that will point to the head.
Print current.data till current points to null.
Current will point to the next node in the list in each iteration.

Program:

  public class CountList {        //Represent a node of the doubly linked list        class Node{          int data;          Node previous;          Node next;            public Node(int data) {              this.data = data;          }      }        //Represent the head and tail of the doubly linked list      Node head, tail = null;        //addNode() will add a node to the list      public void addNode(int data) {          //Create a new node          Node newNode = new Node(data);            //If list is empty          if(head == null) {              //Both head and tail will point to newNode              head = tail = newNode;              //head’s previous will point to null              head.previous = null;              //tail’s next will point to null, as it is the last node of the list              tail.next = null;          }          else {              //newNode will be added after tail such that tail’s next will point to newNode              tail.next = newNode;              //newNode’s previous will point to tail              newNode.previous = tail;              //newNode will become new tail              tail = newNode;              //As it is last node, tail’s next will point to null              tail.next = null;          }      }        //countNodes() will count the nodes present in the list      public int countNodes() {          int counter = 0;          //Node current will point to head          Node current = head;            while(current != null) {              //Increment the counter by 1 for each node              counter++;              current = current.next;          }          return counter;      }        //display() will print out the elements of 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(“Nodes of doubly linked list: “);          while(current != null) {              //Prints each node by incrementing the pointer.                System.out.print(current.data + ” “);              current = current.next;          }      }        public static void main(String[] args) {            CountList dList = new CountList();          //Add nodes to the list          dList.addNode(1);          dList.addNode(2);          dList.addNode(3);          dList.addNode(4);          dList.addNode(5);            //Displays the nodes present in the list          dList.display();            //Counts the nodes present in the given list          System.out.println(“nCount of nodes present in the list: ” + dList.countNodes());      }  }  

Output:

Nodes of doubly linked list:   1 2 3 4 5   Count of nodes present in the list: 5

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Java program to create a doubly linked list of n nodes and count the number of nodes

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