Java - Doubly Linked List Traversal

Traversing through a doubly linked list is very easy. It requires creating a temp node pointing to the head of the list. If the temp node is not null, display its content and move to the next node using temp next. Repeat the process till the temp node becomes null. If the temp node is empty at the start, then the list contains no item.

The function PrintList is created for this purpose. It is a 3-step process.

void PrintList() {
  
  //1. create a temp node pointing to head
  Node temp = new Node();
  temp = this.head;

  //2. if the temp node is not null continue 
  //   displaying the content and move to the
  //   next node till the temp becomes null
  if(temp != null) {
    System.out.print("The list contains: ");
    while(temp != null) {
      System.out.print(temp.data + " ");
      temp = temp.next;
    }
    System.out.println();
  } else {
    
    //3. If the temp node is null at the start, 
    //   the list is empty
    System.out.println("The list is empty.");
  }
}

The below is a complete program that uses above discussed concept to traverse through the doubly linked list and displaying its content.

//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);

    //traverse to display the content of the list.
    MyList.PrintList(); 
  }
}

The above code will give the following output:

The list contains: 10 20 30