Change Label text from different class in java

Question

I have a main gui class which has been made in the NetBeans gui builder. I am creating a mini game where the JLabel timer goes down. The JLabel is located in the main gui and the timer is located in a separate classes called timer for instance. When the loop for the timer is looping, I want the JLabel located in the main gui to change (Timer=10, Timer=9, ...etc).

Review the sample code below for a better understanding.

This is the class where the timer is located:

public class ShapeGame {

Timer timer;
int counter = 10;

ShapeGame() {

    ActionListener a = new ActionListener() {
        public void actionPerformed(ActionEvent e) {

            System.out.println("Counter = " + counter);
            labTimer.setText("Timer: " + counter);
            if (--counter < 0) {
                timer.stop();
                System.exit(0);
            }
        }
    };

    timer = new Timer(1000, a);
    timer.start();
    }
}

This is amended code for where the JLabel is located:

(NOTE: not all code has been added for the JLabel and JFrame just for reading purposes)

public class mainGui extends JFrame {

labTimer = new javax.swing.JLabel();

    private void gameStartStopActionPerformed(java.awt.event.ActionEvent evt) {                                              
        ShapeGame sg = new ShapeGame();
    }
}

I understand this is not the correct way to call the Label from a different class labTimer.setText("Timer: " + counter);. Hope I have provided enough information to help solve this problem.

Answer 1

One possible simple (but not clean) solution is to pass the JLabel into the ShapeGame class so that it can mutate its state directly.

e.g.,

public class ShapeGame {
    Timer timer;
    int counter = 10;

    // note change to constructor parameter
    public ShapeGame(final JLabel label) {
        ActionListener a = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.out.println("Counter = " + counter);

                // note changes
                // labTimer.setText("Timer: " + counter);
                label.setText("Timer: " + counter);

                if (--counter < 0) {
                    timer.stop();
                    System.exit(0);
                }
            }
        };

        timer = new Timer(1000, a);
        timer.start();
    }
}

Then when creating the ShapeGame class, pass the JLabel into its constructor call. Cleaner would be to structure your program a la MVC.