Java - Insert a new node at the end of the Doubly Linked List

In this method, a new node is inserted at the end of the doubly linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the end, the List becomes 10->20->30->100.

Inserting a new node at the end of the doubly linked list is very easy. First, a new node with given element is created. It is then added at the end of the list by linking the last node to the new node.

The function push_back is created for this purpose. It is a 6-step process.

void push_back(int newElement) {
  
  //1. allocate node
  Node newNode = new Node();
  
  //2. assign data element
  newNode.data = newElement;
  
  //3. assign null to the next and prev
  //   of the new node
  newNode.next = null; 
  newNode.prev = null;

  //4. Check the list is empty or not,
  //   if empty make the new node as head 
  if(head == null) {
    head = newNode;
  } else {
    
    //5. Else, traverse to the last node
    Node temp = new Node();
    temp = head;
    while(temp.next != null)
      temp = temp.next;
    
    //6. Adjust the links
    temp.next = newNode;
    newNode.prev = temp;
  }    
}

The below is a complete program that uses above discussed concept to insert new node at the end of the doubly linked list.

//node structure
class Node {
    int data;
    Node next;
    Node prev;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the end of the list
  void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null;
    newNode.prev = null; 
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
      newNode.prev = temp;
    }    
  }

  //display the content of the list
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(temp != null) {
        System.out.print(temp.data + " ");
        temp = temp.next;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }    
};

// test the code 
public class Implementation {
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //Add three elements at the end of the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.PrintList(); 
  }
}

The above code will give the following output:

The list contains: 10 20 30