//main.java
package testabanco;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Connection c = new conecta().getConnection();


        int a = -1;
        while(a!= 0){
        System.out.println("##########Sistema de login###########");
        System.out.println("1 - cadastrar usuario");
        System.out.println("2 - logar");
        System.out.println("3 - atualizar");
        System.out.println("4 - deletar");
        Scanner in = new Scanner(System.in);
        a = in.nextInt();
        switch(a){
            case 1:
         //String sql = "insert into users values(NULL,\"jessica\",\"doida\",\"jessiquita\",\"senhatest\"";

                    String sql = "insert into users values(NULL,?,?,?,?)";
                    Scanner aff = new Scanner(System.in);
                    System.out.print("Digite seu primeiro nome: ");
                    String FirstName = aff.nextLine();
                    System.out.print("Digite seu segundo nome: ");
                    String LastName = aff.nextLine();
                    System.out.print("Digite seu login: ");
                    String username = aff.nextLine();
                    System.out.print("Digite sua senha: ");
                    String password = aff.nextLine();
                    try{
                        PreparedStatement stmt = c.prepareStatement(sql);
                        stmt.setString(1, FirstName);
                        stmt.setString(2, LastName);
                        stmt.setString(3, username);
                        stmt.setString(4, password);

                        stmt.execute();
                        System.out.println("Inserido com sucesso!!");
                        stmt.close();
                    }catch(SQLException e){
                        throw new RuntimeException(e);
                    }

        break;
            case 2:
                    Scanner test = new Scanner(System.in);
                    System.out.println();
                    System.out.println("Entre com o usuario: ");
                    String login = test.nextLine();
                    System.out.println("Entre com a senha: ");
                    String senha = test.nextLine();
                    String sql2 = "select * from users where username = ? and password = ?";

                    try{
                        PreparedStatement stmt = c.prepareStatement(sql2);
                        stmt.setString(1, login);// setstring pq e string ;d
                        stmt.setString(2, senha);


                        ResultSet teste = stmt.executeQuery();
                        if(teste.next() != true){
                            System.out.println("Usuario nao encontrado");
                            System.exit(0);
                        }
                        System.out.println(teste.getString("username"));
                        System.out.println(teste.getString("password"));
                        if(!login.equals(teste.getString("username")) || !senha.equals(teste.getString("username"))){
                            System.out.println("Usuario ou senha invalidos");
                            System.exit(0);
                        }
                        //while(teste.next()){
                        System.out.println("#############Voce esta logado############");
                        System.out.println("ID: "+teste.getString("id"));
                        System.out.println("Username: "+teste.getString("username"));
                        System.out.println("Lastname: "+teste.getString("LastName"));
                        //}
                        stmt.close();
                    }catch(SQLException e){

                        throw new RuntimeException(e);
                    }
                   System.exit(0);
               break;
            case 3:
                 String sql3 = "update users set FirstName = ? where id = 2";
                 Scanner arriegua = new Scanner(System.in);
                 System.out.println("Entre com o novo nome da jessica");
                 String data = arriegua.nextLine();
                    try{
                        PreparedStatement stmt = c.prepareStatement(sql3);
                        stmt.setString(1, data);// setstring pq e string ;d
                        int teste = stmt.executeUpdate();
                        stmt.close();
                    }catch(SQLException e){

                        throw new RuntimeException(e);
                    }
            break;
            case 4:
                 String sql4 = "delete from users where username = ?";
                 Scanner arri = new Scanner(System.in);
                 System.out.println("Entre com o nome a ser deletado");
                 String bata = arri.nextLine();
                    try{
                        PreparedStatement stmt = c.prepareStatement(sql4);
                        stmt.setString(1, bata);// setstring pq e string ;d
                        boolean teste = stmt.execute();
                        stmt.close();
                    }catch(SQLException e){

                        throw new RuntimeException(e);
                    }

        }
    }
    }
}

<!--- conecta.java ---!>
package testabanco;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class conecta {
    public conecta(){
    }
    public Connection getConnection(){
          System.out.println("Conectando ao banco de dados");
          try{
              return DriverManager.getConnection("jdbc:mysql://localhost/universidade","root","aluno");
          }catch(SQLException e){
              throw new RuntimeException(e);
          }
    }

}