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package ivrlib;

import java.beans.Statement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *-
 * @author Jose Ariel, Edwin Quijada
 */
public class Database {

     public static String driver,url,db,usr,pass,server,port;
     public static String error_db="";
     public static Connection conexion;

    public void Conectar(String port,String db, String usr, String pass, String server, String driver)
    {    }

    public void Conectar() {

        // parametros para postgres
        port   ="5432";
        db     = "db_xxxxx";
        usr    = "yyy";
        pass   = "xxxx";
        server = "x.x.x.x";
        driver ="org.postgresql.Driver";
        url    = "jdbc:postgresql://"+server+":"+port+"/"+db;



        try {
            Class.forName(driver).newInstance();
            conexion=DriverManager.getConnection(url,usr,pass);
        } catch (Exception exc){
             System.err.println("** Error de Base de datos en la conexion**\n"+exc.getMessage());
        }
    }

    private void loadDriver()
    {
        try
        {
            Class.forName("org.postgresql.Driver");
        }
        catch (ClassNotFoundException err)
        {
            System.err.println("** Could not load PostgreSQL driver **\n"+exc.getMessage());
            System.exit(1);
        }
    }

    //metodo que retorna un resultset pasandole el query
    public static ResultSet exec_sel(String query){
        try {
            java.sql.Statement comando = conexion.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
            ResultSet rs = comando.executeQuery(query);
            return rs;
        } catch (SQLException ex) {
            Logger.getLogger(Database.class.getName()).log(Level.SEVERE, null, ex);
            System.err.println("** Error de Base de datos, select **\n"+ex.getMessage());
            return null;
        }
    }

    // metodo para ejecutar update, insert o delete
    public void exec_sql(String query){
        try {
            java.sql.Statement stmt = conexion.createStatement();
            stmt.executeUpdate(query);
        } catch (SQLException ex) {
            Logger.getLogger(Database.class.getName()).log(Level.SEVERE, null, ex);
            System.err.println("** Error de Base de datos, insert, update, delete **\n"+ex.getMessage());
        }
    }

    //metodo para obtener la cantidad de registros
    public int CantRegistros(ResultSet ResultSet){
        try {
             int int_cantreg=0;
             while(ResultSet.next()){
                 int_cantreg++;
             }
             return int_cantreg;
         } catch (SQLException ex) {
            Logger.getLogger(Database.class.getName()).log(Level.SEVERE, null, ex);
            return 0;
        }
    }

    public Connection getConexion(){
        return conexion;
    }

    public void CerrarConexion() {
        try {

            conexion.close();
            conexion = null;
        } catch (SQLException ex) {
            Logger.getLogger(Database.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}


When I compile everything is fine but when I run I get this error::
D:\Asterisk-Java\test\ivr>java DBtest
LLamando una clase que esta un mismo paquete
** Error de Base de datos **
org.postgresql.Driver
Exception in thread "main" java.lang.NullPointerException
        at ivrlib.Database.exec_sel(Database.java:61)
        at DBtest.main(DBtest.java:19)

I use this class in DBtest I am a mewbie using JAVA