Thread: Anyone can teach me whats wrong with my program ... (Linked List)

i dont know how to post like others but ... i upload my code ....
can somebody tell whats my problem in my program...
i think after finish doing a method ... the stored data is erased ...

public class Node {
	private Node next;
	private int studNo;
	private String fName;
	private String lName;
 
	public void setNo(int sn){
		studNo = sn;
	}
	public int getNo(){
		return studNo;
	}
	public void setfName(String fn){
		fName = fn;
	}
	public String getfName(){
		return fName;
	}
	public void setlName(String ln){
		lName = ln;
	}
	public String getlName(){
		return lName;
	}
	public void setNext(Node n){
		next = n;
	}
	public Node getNext(){
		return next;
	}
 
 
 
 
 
}

public class SinglyLinkedList {
 
private Node first;
 
public void add(int v , String g , String x){
	Node p = new Node();
	p.setNo(v);
	p.setfName(g);
	p.setlName(x);
	if (first == null){
		first = p;
	} else {
		Node q = first;
		while (q.getNext() !=null){
			q=q.getNext();
		}
		q.setNext(p);
	}
}// end of creating a new node and storing it.
 
 
 
 
 
public void search(int v){
	Node q = first;
 
 
	while (q != null){
		if (v == q.getNo()){
 
			System.out.println("\nFirst Name " + q.getfName() + "\nLast Name " + q.getlName());
		} else {
			q = q.getNext();
		}
 
 
	}//if this is false ... not excute the next statement
 
}// end of searching
 
public String display(){
	String strData = "";
	Node temp = first;
	while (temp != null){
 
		strData =  temp.getNo() + "\t" + temp.getfName() + "\t" + temp.getlName();
	    temp = temp.getNext();
 
	}
	return strData;
 
}// end of displaying a data
 
 
 
}

import java.util.Scanner;
 
public class LabEx1Ruamar {
 
 
	public static void main(String[] args) {
 
    	startPage();//calling a method
    	System.out.println("Program Terminated...");
    }// end of main method
 
 
    public static void startPage(){
    	Scanner input = new Scanner(System.in);
    	char exit = 'Y';
    	do {
    		int x = 0;
 
    		operation();// calling another method
 
    		System.out.print("\nTry again? (y/n): ");
    		String exitType = input.next();
    		do{
    			if (exitType.length()==1){
    				char exitChar = exitType.charAt(0);
    				exit = exitChar;
    				if (exit == 'Y' || exit == 'y' ||
    					exit == 'N' || exit == 'n'){
    						x = 1;
    				}else {
    					System.out.println("Invalid input...\n");
    					System.out.print("Try again? (y/n): ");
    					exitType = input.next();
    					x = 0;
    				}
    			}else {
    				System.out.println();
    				System.out.println("Invalid input...\n");
    				System.out.print("Try again? (y/n): ");
    				exitType = input.next();
    				x = 0;
    			}
    		}while(x==0);
    	}while(exit == 'Y' || exit == 'y');
    }// end of a method
 
 
 
 
   public static void operation(){
   		Scanner input = new Scanner(System.in);
 
   		SinglyLinkedList happy = new SinglyLinkedList();
 
 
		System.out.print("Choose Transaction\n\tA. Enter new student\n\tB. Search student\n\tC. Display all students\n\tD. Exit");
 
		System.out.print("\nEnter Choice: ");
		String p = input.next();
 
		switch(p.charAt(0)){
			case 'A':
				System.out.print("Enter student no: ");
				int boy = input.nextInt();
				System.out.print("Enter first name: ");
				String girl = input.next();
				System.out.print("Enter last name: ");
				String kill = input.next();
				happy.add(boy, girl , kill);// storing it to node
 
 
				System.out.print("SAVED");
				break;
 
			case 'B':
				System.out.print("Enter student no: ");
				int hannah = input.nextInt();
				happy.search(hannah);//searching
				break;	
			case 'C':
				System.out.print("\t" + happy.display());//display
				break;
				//i dont do the letter "D" because something wrong in other cases..
			default:
				System.out.println("Wrong Choice");	
					break;
   }//end of switch case
 
 
   }// end of operation(a method)
 
 
 
 
	}// end of class