Hello i want to ask you where is the problem and my programme give me only null returns ---> package javalab;

import java.sql.*;

public class History {





    private int w ;
    private int v ;
    private int c ;

    public History() {}

    public String findPrevious(){
        Connection conn = null;
        Statement statement = null;
        String SQLStr ;
        String retString = "";
        ResultSet nu =  null;


        SQLStr = "SELECT COUNT(*) AS COS  FROM dev.history WHERE previous like 1; ";
        SQLStr = "SELECT COUNT(PREVIOUS) AS VOD FROM dev.history WHERE PREVIOUS like 2; ";
        SQLStr = "SELECT COUNT(PREVIOUS) AS WIN FROM dev.history WHERE PREVIOUS like 3 ;";


        try{
            Class.forName("com.mysql.jdbc.Driver").newInstance();

            conn = DriverManager.getConnection("jdbc:mysql://"+
                    "localhost:3306/dev","root","pro");



            statement = conn.createStatement();
            nu = statement.executeQuery(SQLStr);

            if (nu.next())
                c = nu.getInt("COUNT(previous)");
                v = nu.getInt("VOD"); 
                w = nu.getInt("WIN");

        }catch (SQLException sqlEx){
            System.err.println(sqlEx.getMessage());
        }catch (ClassNotFoundException classNotFound){
            System.err.println(classNotFound.getMessage());
        }catch (Exception ex){
            System.err.println(ex.getMessage());
        }finally {
            try
                {if (statement != null){
                    statement.close();
                }
            }catch(final SQLException sqlEx){
                System.err.println(sqlEx.getMessage());
            }
        }
        return retString;
    }

        public int Wind(){
            return w;
        }

        public int Vodafone(){
            return v;
        }
        public int Cosmote(){
            return c;
        }

} thx a lot in advance !!