JAVA - Swing-free timer with MVC

Question

I’m studying java and I saw myself in a situation that I don’t know how to solve... I have a timer where I intend to do it following the rules of MVC, but I can’t update Jlabel when I separate the code Timer from View.

I believe I have to use Threads. It has an easier way that is with swing.Timer however, I would like to separate the logic of the interface so I can use the same model in java android when I make the mobile version.

When I click the 'start' button the application hangs.

Simple GUI with two buttons

package source;
import source.Pomodoro;

public class GUI extends javax.swing.JFrame {
    private Pomodoro pomodoro;
public GUI() {
        initComponents();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        lbContadorTempo = new javax.swing.JLabel();
        btIniciar = new javax.swing.JButton();
        btZerar = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new javax.swing.BoxLayout(getContentPane(), javax.swing.BoxLayout.LINE_AXIS));

        lbContadorTempo.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
        lbContadorTempo.setText("00:00:00");
        getContentPane().add(lbContadorTempo);

        btIniciar.setText("Iniciar");
        btIniciar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btIniciarActionPerformed(evt);
            }
        });
        getContentPane().add(btIniciar);

        btZerar.setText("Zerar");
        btZerar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btZerarActionPerformed(evt);
            }
        });
        getContentPane().add(btZerar);

        pack();
    }// </editor-fold>                        

    private void btIniciarActionPerformed(java.awt.event.ActionEvent evt) {                                          
        pomodoro = new Pomodoro();

        pomodoro.iniciar();        
        lbContadorTempo.setText(pomodoro.getTempo()); // altera o JLabel

    }                                         

    private void btZerarActionPerformed(java.awt.event.ActionEvent evt) {                                        


    }                                       

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new GUI().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btIniciar;
    private javax.swing.JButton btZerar;
    private javax.swing.JLabel lbContadorTempo;
    // End of variables declaration                   
}

Model

   package source;


import java.awt.EventQueue;
import java.util.Timer;
import java.util.TimerTask;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JOptionPane;

public class Pomodoro {
    private Timer tm;
    private int tempo = 5; // segundos
    private boolean ligado = false;


    public Pomodoro() {

    }
    public void iniciar() {
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {
          public void run() {
            tempo++;
           System.out.println(tempo);
          }
        }, 1000, 1000);

    }
    public void setTempo(int tempo) {
        tempo++;

    }
    public String getTempo() {
        return String.format("%02d", tempo);

    }

}

Answer 1

import javax.swing.*;

public class GUI extends javax.swing.JFrame{
    private Pomodoro pomodoro;
    boolean cronometroIniciar = true;
    Thread t = null;

public GUI() {
        initComponents();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        lbContadorTempo = new javax.swing.JLabel();
        btIniciar = new javax.swing.JButton();
        btParar = new javax.swing.JButton();
        btZerar = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(new javax.swing.BoxLayout(getContentPane(), javax.swing.BoxLayout.LINE_AXIS));

        lbContadorTempo.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
        lbContadorTempo.setText("00:00:00");
        getContentPane().add(lbContadorTempo);

        btIniciar.setText("Iniciar");
        btIniciar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btIniciarActionPerformed(evt);
            }
        });
        getContentPane().add(btIniciar);

        btParar.setText("Parar");
        btParar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btPararActionPerformed(evt);
            }
        });
        getContentPane().add(btParar);

        btZerar.setText("Zerar");
        btZerar.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btZerarActionPerformed(evt);
            }
        });
        getContentPane().add(btZerar);

        pack();
    }// </editor-fold>                        

    private void btIniciarActionPerformed(java.awt.event.ActionEvent evt) { 
        cronometroIniciar = true;   
        pomodoro = new Pomodoro();
        pomodoro.iniciar();  
        t = new Thread(() ->{
        while(cronometroIniciar){ //status true quando aperta o botão iniciar
            lbContadorTempo.setText(pomodoro.getTempo()); // altera o JLabel
        }
        });
        t.start();
    }  

    private void btPararActionPerformed(java.awt.event.ActionEvent evt) {  
        System.out.println("Parar");
        cronometroIniciar = false;
        pomodoro = new Pomodoro();
        pomodoro.parar(); 
        t.interrupt();
    }

    private void btZerarActionPerformed(java.awt.event.ActionEvent evt) {                                        


    } 



    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(GUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new GUI().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btIniciar;
    private javax.swing.JButton btParar;
    private javax.swing.JButton btZerar;
    private javax.swing.JLabel lbContadorTempo;
    // End of variables declaration                   
}

import java.awt.EventQueue;
import java.util.Timer;
import java.util.TimerTask;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.*;

public class Pomodoro {
    private Timer tm = new Timer();
    private int tempo = 5; // segundos
    private static boolean ligado = true;

    public Pomodoro() {

    }

    public void iniciar() {
        ligado = true;
        tm.scheduleAtFixedRate(new TimerTask() {
          public void run() {             
                if(ligado) {
                    tempo++;
                    System.out.println(tempo);    
                } else {
                   tm.cancel();
                   tm.purge();
                }

          }
        }, 1000, 1000);
    }

    public void parar() {
        System.out.println("parouuuu");
        ligado  = false;
    }

    public void setTempo(int tempo) {
        tempo++;

    }
    public String getTempo() {
        return String.format("%02d", tempo);

    }

}

Answer 2

    private void btIniciarActionPerformed(java.awt.event.ActionEvent evt) {                                          
        pomodoro = new Pomodoro();
        pomodoro.iniciar();  
        Thread t = new Thread(() ->{
        while(true){ //status true quando aperta o botão iniciar
            lbContadorTempo.setText(pomodoro.getTempo()); // altera o JLabel
        }
        });
        t.start();
    }