Java program to delete a new node from the beginning of the doubly linked list

by Online Tutorials Library July 22, 2022

Java program to delete a new node from the beginning of the doubly linked list

In this program, we will create a doubly linked list and delete a node from the beginning of the list. If the list is empty, print the message “List is empty”. If the list is not empty, we will make the head to point to next node in the list then; we will delete the first node.

Consider the above example, new was the head of the list. Make head to point to next node in the list. Now, node 1 will become the new head of the list thus, deleting node new.

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.
deleteFromStart() will delete a node from the beginning of the list:
- It first checks whether the head is null (empty list) then, it will return from the function as there is no node present in the list.
- If the list is not empty, it will check whether the list has only one node.
- If the list has only one node, it will set both head and tail to null.
- If the list has more than one node then, the head will point to next node in the list and delete the old head node.

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 DeleteStart  {        //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;          }      }        //deleteFromStart() will delete a node from the beginning of the list      public void deleteFromStart() {          //Checks whether list is empty          if(head == null) {              return;          }          else {              //Checks whether the list contains only one element              if(head != tail) {                  //head will point to next node in the list                  head = head.next;                  //Previous node to current head will be made null                  head.previous = null;              }              //If the list contains only one element              //then, it will remove node and now both head and tail will point to null              else {                  head = tail = null;              }          }      }        //display() will print out the nodes 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;          }          while(current != null) {              //Prints each node by incrementing the pointer.                System.out.print(current.data + ” “);              current = current.next;          }          System.out.println();      }        public static void main(String[] args) {            DeleteStart dList = new DeleteStart();          //Add nodes to the list          dList.addNode(1);          dList.addNode(2);          dList.addNode(3);          dList.addNode(4);          dList.addNode(5);            //Printing original list          System.out.println(“Original List: “);          dList.display();          while(dList.head != null) {              dList.deleteFromStart();              //Printing updated list              System.out.println(“Updated List: “);              dList.display();          }      }  }  

Output:

Original List:   1 2 3 4 5   Updated List:   2 3 4 5   Updated List:   3 4 5   Updated List:   4 5   Updated List:   5   Updated List:   List is empty

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Java program to delete a new node from the beginning of the doubly linked list

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