Q:

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

belongs to collection: Java Doubly Linked List Programs

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.
• 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;
}
}

//Create a new node
Node newNode = new Node(data);

//If list is empty
//Both head and tail will point to newNode
//head's previous will point to 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

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
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();

//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```