I don’t Know why I am getting runtime errors
import java.util.*;
public class Main{
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
Scanner scn = new Scanner(System.in);
int t = scn.nextInt();
while(t > 0){
LinkedList list1 = new LinkedList();
int n1 = scn.nextInt();
for (int j = 0; j < n1; j++) {
int item = scn.nextInt();
list1.addLast(item);
}
LinkedList list2 = new LinkedList();
int n2 = scn.nextInt();
for (int j = 0; j < n2; j++) {
int item = scn.nextInt();
list2.addLast(item);
}
list1.merge_sorted_list(list2);
list1.display();
System.out.println();
t--;
}
}
}
class LinkedList {
private class Node {
int data;
Node next;
}
private Node head;
private Node tail;
private int size;
public int getFirst() throws Exception {
if (this.size == 0)
throw new Exception("linked list is empty");
return head.data;
}
public int getLast() throws Exception {
if (this.size == 0)
throw new Exception("linked list is empty");
return tail.data;
}
public void addLast(int item) {
// create a new node
Node nn = new Node();
nn.data = item;
nn.next = null;
// update summary
if (size == 0) {
this.head = nn;
this.tail = nn;
size++;
} else
{
this.tail.next = nn;
this.tail = nn;
size++;
}
}
public void addFirst(int item) {
Node nn = new Node();
nn.data = item;
nn.next = null;
if (size == 0) {
this.head = nn;
this.tail = nn;
size++;
} else {
nn.next = this.head;
this.head = nn;
size++;
}
}
public int removeFirst() throws Exception {
Node fn = this.head;
if (this.size == 0)
throw new Exception("linked list is empty");
if (this.size == 1) {
this.head = null;
this.tail = null;
size = 0;
} else {
Node np1 = this.head.next;
this.head = np1;
size--;
}
return fn.data;
}
public void merge_sorted_list(LinkedList other) throws Exception {
Node head1 = head;
Node head2 = other.head;
if(head1 == null)
{
head = head2;
return;
}
else if(head2 == null)
{
return;
}
Node head3 = null;
if(head1.data < head2.data)
{
head3 = head1;
head1 = head1.next;
}
else
{
head3 = head2;
head2 = head2.next;
}
Node current = head3;
while(head1 != null && head2 != null)
{
if(head1.data<head2.data)
{
current.next = head1;
head1 = head1.next;
}
else if(head2.data < head1.data){
current.next = head2;
head2 = head2.next;
}
// else
// {
// current.next = head2;
// head2 = head2.next;
// head1 = head1.next;
// }
current = current.next;
}
if(head1 == null)
current.next = head2;
else
current.next = head1;
head = head3;
}
public void display() {
Node temp = this.head;
while (temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
}
}