ResultSet first does not work

I'm creating a Java application in Eclipse.

I'm having trouble making the First, Previous, Next, and Last buttons work.

I'm stuck on the First button because, I believe, the difference is just the .first() , .next() , .previous() and .last() .

The error that appears when I click the button is this:

  

java.sql.SQLException: Invalid operation to forward only   result set: first

The Aluno table has the fields ra and nome , both are varchar2 .

When I click the First button this will activate this method:

public void primeiro() {
    try {
        //con é meu objeto da classe ConexaoMVC
        con.conecta();

        ResultSet rs;
        String RA,NOME;

        rs = con.stm.executeQuery("Select * from Aluno");
        rs.first();

        RA = rs.getString("ra");
        NOME = rs.getString("nome");
        // visao é o objeto da minha classe de interface grafica
        visao.setRA(RA);
        visao.setNome(NOME);

    } catch(SQLException SqlExc){ //trata os erros
        System.out.println("Erro de SQL! \n"+SqlExc);      
    }
}

Code of my connection class:

package bd;

import java.sql.*;
import javax.swing.*;

public class ConexaoMVC {
    public Connection conexao;
    private String driver, url;
    Statement stm;

    public ConexaoMVC() {
        //driver="sun.jdbc.odbc.JdbcOdbcDriver";
        driver = "oracle.jdbc.driver.OracleDriver";
        url = "jdbc:oracle:thin:guilherme/1997@//localhost:1521/XE";
    }

    public void conecta() {
        try {
            // carrega o driver da ponte jdbc-odbc
            Class.forName(driver);
            // abre conexao com o banco de dados
            conexao = DriverManager.getConnection(url);
            System.out.println("Conexão executada com sucesso");

            stm = conexao.createStatement();
            //conexao.close();
        } catch (SQLException SqlExc) {
            System.out.println("Erro de SQL!");
        } catch (ClassNotFoundException exc) {
            System.out.println("Classe não encontrada!");
        }
    }

    public static void main(String args[]) {
        Conexao ins = new Conexao();
    }
}

Sets Code:

public void setRA(String ra) {
    jtfRa.setText(ra);
}

public void setNome(String nome) {
    jtfNome.setText(nome);
}