How can I get my next pointer of my LinkedList class without using built in function?

I'm newbie in programming and I'm practicing a Java Programming Language. I was having a rough day in finding the solution of my program because I cannot get my "next" pointer and I really want to print my last value. Could someone help me to fix this and explain to me? Thank you in advance. Here's my code.

Note: The output of my program is 5.

public class Node {
private int data;
private Node next;
public Node (int data){
this.data = data;
}
public int getData() {
return this.data;
}
public void setNext(Node n) {
this.next = n;
}
public Node getNext() {
return this.next;
}
}
public class LinkedList {
private static Node head, next;
public LinkedList (int data) {
head = new Node (data);
}
public void addLast(int data) {
Node n = new Node (data);
if (head == null) {
head = n;
}
else {
Node temp = head;
temp.setNext(next);
while (temp.getNext() != null) {
temp = temp.getNext();
}
Node t = temp.getNext();
t = n;
}
}
public void printList() {
head.setNext(next);
while (head.getNext() != null) {
System.out.println(head.getData());
head = head.getNext();
}
System.out.println(head.getData());
}
public static void main(String[] args) {
LinkedList l = new LinkedList(5);
l.addLast(7);
l.printList();
}
}

TL;DR:

1. You set null as the next node in your printList() method;
2. Your addLast does not work either (you do not set the next node (see details below);
3. You should never set the node (or do any logical alteration whatsoever) in your print method. Print must just print, as the name suggests, and it should not contain any side-effect, amending your data structure. That is: you have to clearly separate your concerns.

In your current addLast, you do:

public void addLast(int data) {
    Node n = new Node (data);

    if (head == null) {
        head = n;
    }
    else {
        Node temp = head;
        temp.setNext(next);
        while (temp.getNext() != null) {
            temp = temp.getNext();
        }
        Node t = temp.getNext();
        t = n;
    }
}

which means, that when your temp's next node is null, you never add the Node you instantiate with your int argument.

Change the else block as follows:

else {
    Node temp = head;
    temp.setNext(next);
    while (temp.getNext() != null) {
        temp = temp.getNext();
    }
    temp.setNext(n);
    //two redundant lines removed
}

Correspondingly, remove head.setNext(next); (and possibly unnecessary System.out.println() statement) from your printList() method.

P. S. I would really recommend you to spend some time on the Linked List Data Structure (Data Structure, and not the Java code), as your current design, shows that you need to have a better grasp of it.

I suggest following two amendment to your code.

1. with following else block in addLast method.

        Node temp = head;
   temp.setNext(next); // this line causing the next object to be set to null all the time. commenting this line will help in making sure the follwing loop reaches to end of the list, otherwise the while loop will always exit without any iteration.
   while (temp.getNext() != null) {
   temp = temp.getNext();
   }
   Node t = temp.getNext(); 
   t = n; // this will also not change the linking. Its basically assigned a new value to t.
   

use following suggestion

        Node temp = head;
while (temp.getNext() != null) {
temp = temp.getNext();
}
// now we reached end of list and temp.next is null.
// assign newly createdd node to temp.next
temp.setNext(n);

2. While iterating the element in printList same problem exist as mentioned in point 1. try to use following suggestion for printList method.
   <pre><code>
   // head.setNext(next); // This line will always set head.next to null and whole list will be lost. Instead of this use following line
   Node temp = head;
   while (temp.getNext() != null) { // here if you use head its position will move to end. So use temp variable for iteration
   System.out.println(temp.getData());
   temp= temp.getNext();
   }
   System.out.println(temp.getData());
   </code></pre>
   You may also need to study list iteration algorithm to have better understanding.

I've made some amendments to make your code work. The If statement in your addLast method:

if (head == null) {

is redundant since your LinkedList can only be initialized by passing some data, hence head will never be null, it will always point to the Node containing data

Also the line

head.setNext(next);

in your printList() was problematic, it was always pointing to null

public class LinkedList {
private static Node head, next;
public LinkedList(int data) {
head = new Node(data);
}
public void addLast(int data) {
Node n = new Node(data);
Node temp = head;
temp.setNext(next);
while (temp.getNext() != null) {
temp = temp.getNext();
}
temp.setNext(n);
}
public void printList() {
while (head.getNext() != null) {
System.out.println(head.getData());
head = head.getNext();
}
System.out.println(head.getData());
}
public static void main(String[] args) {
LinkedList l = new LinkedList(5);
l.addLast(7);
l.printList();
}
}