MVC and JAVA doubt

Question

Giving continuity to a project of the college that was stopped, I intend to do it in Java already I did and I remade from scratch about 2 times however, it was horrible and to each class I realized that I could do better, so I decided to try to organize the code using MVC.

My question is, why is this code not working? It’s been about three days that I’m reading the stackoverflow and so far I haven’t found the problem.

I’m using this tutorial as a basis: http://www.gqferreira.com.br/artigos/ver/mvc-com-java-desktop-parte3

Model

     package duvidamvc;

    import javax.swing.JOptionPane;

    public class DuvidaModel {
        // Construtor
        public DuvidaModel() {
            iniciar();
        }

        public void iniciar() {
            JOptionPane.showMessageDialog(null, "Funcionou.");
        }
    } //aqui tinha uma chave sobrando 

Controller

   package duvidamvc;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class DuvidaController implements ActionListener {
    private DuvidaView view;
    private DuvidaModel modelo;

    // Construtor
    public DuvidaController(DuvidaView view) {
        this.view = view;
        this.view.getBtUm().addActionListener(this);
        this.view.getBtDois().addActionListener(this);
        this.view.getBtTres().addActionListener(this);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == this.view.getBtUm()) {
            chamandoModel();
        }
        if (e.getSource() == this.view.getBtDois()) {
            chamandoModel();
        }
        if (e.getSource() == this.view.getBtTres()) {
            chamandoModel();
        }
    }

    private void chamandoModel() {

        modelo = new DuvidaModel();
        modelo.iniciar();
    }
}

View

    package duvidamvc;
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JPanel;

    public class DuvidaView extends JFrame {
        // Encapsulamento
        private JFrame tela;
        private JPanel painel;
        private JButton btUm;
        private JButton btDois;
        private JButton btTres;

        // Construtor
        public DuvidaView() {
            janela();
        }

        public JButton getBtUm() {
            return btUm;
        }

        public JButton getBtDois() {
            return btDois;
        }

        public JButton getBtTres() {
            return btTres;
        }

        public void janela() {
            JFrame tela = new JFrame();
            painel = new JPanel();
            // painel.setLayout(null);
            tela.setTitle("Duvida padrão MVC");
            tela.setDefaultCloseOperation(EXIT_ON_CLOSE);
            tela.add(painel);
            tela.setSize(400, 80);
            btUm = new JButton("Exemplo 1");
            painel.add(btUm);
            btDois = new JButton("Exemplo 2");
            painel.add(btDois);
            btTres = new JButton("Exemplo 3");
            painel.add(btTres);
            tela.setVisible(true);
            pack();
        }

        public static void main(String[] args) {
            new DuvidaView();
        }
    }

Answer 1

First, if you put one JOptionPane on your model, you are already violating MVC. Swing components are things from the view. Do not put anything referencing any user interface in the model.

Second, that you should only have one model. But how are you instantiating the model within the method chamandoModel and this same method ends up dropping the model to the garbage collector, once again you violated the MVC. The controller is used to paste the view into the model and not to create and recreate the model whenever an action is executed. The field private DuvidaModel modelo; which is what you should probably use, you’re not using.

Third, that DuvidaController implements ActionListener It’s bad programming practice. Plus you play control of all buttons in the same method to then separate with a lot of ifs, which is another bad programming practice. Give a method to each button and do not mix them.

Fourth, do not violate the view encapsulation in the controller. The view should warn the controller, not the controller access the view components to inject itself there.

Fifth, or you use extends JFrame or else you create the JFrame with new. The two together don’t make sense.

So your code could be this:

package duvidamvc;

public class DuvidaModel {

    public DuvidaModel() {
    }

    public String fazerAlgumaCoisa(int n) {
        return "Funcionou " + n + ".";
    }
}

package duvidamvc;

public class DuvidaController {
    private final DuvidaView view;
    private final DuvidaModel modelo;

    public DuvidaController(DuvidaModel modelo) {
        this.modelo = modelo;
        this.view = new DuvidaView(this);
    }

    public String clicouBotao1() {
        return modelo.fazerAlgumaCoisa(1);
    }

    public String clicouBotao2() {
        return modelo.fazerAlgumaCoisa(2);
    }

    public String clicouBotao3() {
        return modelo.fazerAlgumaCoisa(3);
    }
}

package duvidamvc;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class DuvidaView {

    public DuvidaView(DuvidaController controller) {
        JFrame tela = new JFrame();
        painel = new JPanel();
        //painel.setLayout(null);
        tela.setTitle("Duvida padrão MVC");
        tela.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        tela.add(painel);
        tela.setSize(400, 80);

        btUm = new JButton("Exemplo 1");
        painel.add(btUm);
        btUm.addActionListener(e -> JOptionPane.showMessageDialog(null, controller.clicouBotao1()));

        btDois = new JButton("Exemplo 2");
        painel.add(btDois);
        btDois.addActionListener(e -> JOptionPane.showMessageDialog(null, controller.clicouBotao2()));

        btTres = new JButton("Exemplo 3");
        painel.add(btTres);
        btTres.addActionListener(e -> JOptionPane.showMessageDialog(null, controller.clicouBotao3()));

        tela.setVisible(true);
        tela.pack();
    }
}

package duvidamvc;

public class Principal {
    public static void main(String[] args) {
        DuvidaModel m = new DuvidaModel();
        new DuvidaController(m);
    }
}