What is wrong in my code?

public class mergetwosortedLL {

private class node {
	int data;
	node next;
	public int size;
}
private node head;
private node tail;
private int size;

public void display() {
	node temp = this.head;
	while (temp != null) {
		System.out.print(temp.data + ", ");
		temp = temp.next;
	}
}
public void addlast(int item) {
	node nn = new node();
	nn.data = item;
	nn.next = null;
	if (this.size >= 1) {
		this.tail.next = nn;

	}
	if (this.size == 0) {
		this.head = nn;
		this.tail = nn;
		this.size++;
	} else {
		this.tail = nn;
		this.size++;
	}
}


public static void main(String[] args) {
	Scanner scn=new Scanner(System.in);
	int t=scn.nextInt();
	for (int i=0;i<t;i++) {
		int n1=scn.nextInt();
		mergetwosortedLL list1=new mergetwosortedLL();
		for(int j=0;j<n1;j++) {
			int a=scn.nextInt();
			list1.addlast(a);
		}
		int n2=scn.nextInt();
		mergetwosortedLL list2=new mergetwosortedLL();
		for(int j=0;j<n2;j++) {
			int b=scn.nextInt();
			list2.addlast(b);
		}
		mergetwosortedLL list=mergetwosortLL( list1,list2);
		list.display();
		
		
	}
	
}
public static mergetwosortedLL mergetwosortLL(mergetwosortedLL list1,mergetwosortedLL list2) {
	mergetwosortedLL merged=new mergetwosortedLL();
	node one= list1.head;
	node two=list2.head;
	while (one !=null && two!=null) {
		if (one.data <two.data) {
			merged.addlast(one.data);
			one=one.next;
			
		}
		else {
			merged.addlast(two.data);
			two=two.next;
		}
		
		
	}
	if (one ==null) {
		while (two!=null) {
			merged.addlast(two.data);
			two=two.next;
			
		}
	}
	if (two ==null) {
		while (one!=null) {
			merged.addlast(one.data);
			one=one.next;
			
		}
	}
	return merged;
}

}

@harsh.hj bro i have already given you the corrected code in previous thread, just check that thread, that is your code that i have corrected.
And if there is no further query then mark both threads as resolved else feel free to ask buddy!