Is there a workaround to classes calling each other?

Question

I am trying to use JavaFX to code a stopwatch. But I am pretty new to java and still have problems to really understand OOP. I need to have to classes calling each others methods. I know that static methods and variables should be avoided. The gui has buttons start and stop which should start and stop the timer. I have a "TimerClass" set up. There is a method inside which runs code every second when it has been activated once. So when I hit the start button I want that to happen. This seems to work already. But every second the variable "secondsPassed" is updated the label on my gui needs to be updated as well.

I could make the lblTime Button and the corresponding method static. Also I heard about about setting the constructors in a way that you can make every instance be equal to another existing instance. But I still do not understand it enough to be able to use it. (Java: classes with instance of each other) I also tried creating a "helper class". This was to avoid having to instance two classes from one another. But the helper class would have still been another instance of "TimerClass". I have some code to show what I have tried so far.

package application;

import application.TimerClass;

import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.Label;

public class Controller {
    TimerClass timerClass = new TimerClass();

    @FXML
    Button btnStart;
    @FXML
    Button btnPause;
    @FXML
    Label lblTime;

    public void btnStartAction() {
        timerClass.timerStart();
    }

    public void btnPauseAction() {
        timerClass.timerPause();
    }

    public void setLblTime(int input) {
        lblTime.setText(""+input);
    }

}

package application;

import application.Controller;
import application.Helper;

import java.util.Timer;
import java.util.TimerTask;

public class TimerClass {
    static int secondsPassed = 0;

    Controller controller = new Controller();
    TimerClass timerClass = new TimerClass();
    Helper helper;

    public TimerClass(TimerClass input){
        this.helper = timerClass;
    }

    public TimerClass() {

    }

    Timer mytimer = new Timer();
    TimerTask timerTask = new TimerTask() {

        @Override
        public void run() {
            secondsPassed++;
            System.out.println("" + secondsPassed);
        }
    };

    public void timerStart() {
        mytimer.scheduleAtFixedRate(timerTask, 1000, 1000);
    }

    public void timerPause() {
        mytimer.cancel();
    }

    public int getSecondsPassed() {
        return secondsPassed;
    }

}

Thanks in advance!

Answer 1

You don't need to instance the classes from one another. In fact this would be a bad idea, since it the instance of the Controller class is a different one to the one used with your scene.

Instead you should pass the existing class to your TimerClass. (Note that you may want to "hide" the Controller behind a interface to make the TimerClass more reuseable.)

public class TimerClass {
    // don't make this static
    // otherwise you won't be able to use multiple instances at the same time
    volatile int secondsPassed = 0; 

    private final Controller controller;


    public TimerClass(Controller controller) {
        this.controller = controller;
    }

    TimerTask timerTask = new TimerTask() {

        @Override
        public void run() {
            secondsPassed++;
            // update on the JavaFX application thread
            Platform.runLater(() -> controller.setLblTime(secondsPassed));
        }
    };

    public void timerStart() {
        mytimer.scheduleAtFixedRate(timerTask, 1000, 1000);
    }

    public void timerPause() {
        mytimer.cancel();
    }

    public int getSecondsPassed() {
        return secondsPassed;
    }

}

public class Controller {
    TimerClass timerClass = new TimerClass(this);
    ...
}

---

You may want to take a look at the first suggestion in the following answer though: https://stackoverflow.com/a/9966213/2991525

Answer 2

Hey Leonhard great job so far, seems you have a decent understanding of things so far. Let me know if I understand the problem correctly, so you have a button that you press called 'start'. That button makes the seconds start ticking by, and in addition you have a label that displays the seconds that are going by, but the label doesn't update to show the current seconds?

The first thing that comes to mind is setting a boolean value for the start button.

if (** when the user clicks the button **) {
      buttonBoolean = !buttonBoolean; //this just turns false to true; and true to false.
}

Then in the method that adds the seconds, make an 'if' statement to check if the start button is on.

if (buttonBoolean == true) {
    seconds++;
    setLabelValue = seconds;
}

If it is true, then update the seconds and set the value of the label to the updated value.

Let me know if this helps!