I need help with linked list in java [Data structures]

Question

Hello everyone, I inserted a new node at the beginning of the linked list but i am not able to print it's data. It still says null

Please guide me where i am doing wrong. Thank you!

//initial head
head = null
//after inserting node - 30 at the beginnnig

[30]-->null
|
head

//after inserting node - 20 at the beginnnig
[20]-->[30]-->null
|
head

//after inserting node - 10 at the beginnnig

[10]-->[20]-->[30]-->null
|
head

Code:
https://code.sololearn.com/cmYn9tuKj7Ng

Answer 1

Edwin Simply pass the newly created temp node to the head in the function before returning.

https://code.sololearn.com/c1bi2PzuFQZc

Answer 2

your idea is this:

Node temp = new Node(x);
temp.next = head;
head = temp; // added
return head;

then print
System.out.println(head.data);
System.out.println(head.next.data);
System.out.println(head.next.next.data);

Answer 3

you are passing object head of null value and getting same head object which is null.

Node head = new Node(2);
first create a head node.. you get 2 as output..

or else

if you return temp, you get last object value 50.

Answer 4

Jayakrishna🇮🇳 initially node head can be defined as null. It doesn't really has to be set with a value always.

Check out this

https://www.log2base2.com/data-structures/linked-list/inserting-a-node-at-the-beginning-of-a-linked-list.html

Answer 5

@Jayakrishna🇮🇳
I'm expecting the last node value to be printed i.e 50

head = insertStart(head, 23);
head = insertStart(head, 30);
head = insertStart(head, 50);

Even if I create a node with a value at the start, it's value isn't changing.

If i understand you correctly:

Node head = new Node(2);
head = insertStart(head, 23);
head = insertStart(head, 30);
head = insertStart(head, 50);
System.out.println(head.data);
//it prints 2 because the head reference is not changed

Answer 6

@zemiak Yes, you are right. I figured it out thank you.

Answer 7

Lambda you may not understood my point. It should get a head.data value immediately after a node inserted. But op code is null all time.

initially any node is null default, not only head..!!

Edwin
Yes.
head = temp ; will solve the problem..
But you replacing previous head data with current one I think..
So you may get trouble in access later I think..

Hope it helps..

Edit:

Oh. It solved. 👍

Answer 8

@Jayakrishna🇮🇳 initially node is defined as null. While inserting the values at the beginning of the linked list head changes its next reference to the return node by temp node.

Answer 9

Yes. But head also need to set a value for its data.. If head have no data, then it's no meaning to creates nodes.. what is your expected head.data value?