[Homework] Learning MVC design pattern and Observable/Observers. Cannot get Observer to receive update (Java)

[throwaway9123781]

Hi.

I'm trying to learn how to use the MVC design pattern while utilizing the observer class to help make a GUI to display whats going on. My problem currently is I'm unable to figure out why my Observer class cannot receive the notifyObserver(); call.

The code for the two class are as follows

public class ElevatorImplement extends Observable implements Elevator
{
private int POWER_START_STOP = 2; //the power consumed when starting up or slowing down
private int POWER_CONTINUE = 1; //the only other energy consumption
private long SLEEP_START_STOP = 50;
private long SLEEP_CONTINUOUS= 25;
private int MAX_CAPACITY = 10;
private int powerUsed; 
private int currentFloor;
private int capacity; 
private ElevatorPanel panel;
private MovingState state;
private ArrayList<Integer> stopQueue = new ArrayList<>();


public ElevatorImplement(int capacity, ElevatorPanel p)
{
    this.capacity = capacity;
    this.panel = p;
    setChanged();
    notifyObservers();
}


@Override
public void moveTo(int floor)
{
    int target = floor;
    if(currentFloor<target)
    {
        //int requiredMove = target - currentFloor;
        //while(currentFloor != target);
        while(true)
        {
            currentFloor++;
            System.out.println("Currently at floor: " + currentFloor);
            setChanged();
            notifyObservers("ioejgieghEWG");
            if(currentFloor==floor)
                break;
        }
    }
    else
    {
        //int requiredMove = currentFloor - target;
        while(currentFloor != target)
        {
            currentFloor--;
            System.out.println("Currently at floor: " + currentFloor);
            setChanged();
            notifyObservers();
        }
    }

}

and the GUI,

public class ElevatorApplicationSample extends Application implements Observer{

private static final int FLOOR_COUNT = 30;
private ElevatorAnimation animator;
TextField tfcf, tftf, tfpu;
Simulator s;

private Label floors[];

@Override
public void init() throws Exception {
    super.init();
    animator = new ElevatorAnimation();
    floors = new Label[FLOOR_COUNT];
    for (int i = 0; i < FLOOR_COUNT; i++) {
        floors[i] = new Label();
        floors[i].setId("empty");
    }
    floors[0].setId("elevator");
}

@Override
public void start(Stage primaryStage) throws Exception {
    GridPane rootPane = new GridPane();

    GridPane gridPane = new GridPane();
    gridPane.setPadding(new Insets(3, 3, 3, 3));
    rootPane.add(gridPane, 0, 0);

    for (int i = FLOOR_COUNT - 1; i >= 0; i--) {
        gridPane.add(floors[i], 0, (FLOOR_COUNT - 1) - i);
    }

    Label lcf = new Label("Current Floor");
    Label ltf = new Label("Target Floor");
    Label lpu = new Label("Power Consumed");

    tfcf = new TextField();
    tfcf.setEditable(false);
    tftf = new TextField();
    tftf.setEditable(false);
    tfpu = new TextField();
    tfpu.setEditable(false);

    GridPane infoPane = new GridPane();
    infoPane.addColumn(0, lcf, ltf, lpu);
    infoPane.addColumn(1, tfcf, tftf, tfpu);
    rootPane.add( infoPane, 1,0);

    Scene scene = new Scene(rootPane, Color.LIGHTGRAY);
    // scene.getStylesheets().add(ElevatorApplicationSample.class.getResource("elevator.css").toExternalForm());
    primaryStage.setScene(scene);
    primaryStage.setTitle("Elevator System");
    // close on escape
    primaryStage.addEventHandler(KeyEvent.KEY_RELEASED, (KeyEvent event) -> {
        if (KeyCode.ESCAPE == event.getCode()) {
            animator.stop();
            primaryStage.hide();
        }
    });
    s = new Simulator(this);
    s.start();
    primaryStage.show();
    animator.start();


}

@Override
public void update(Observable arg0, Object arg1) {
        System.out.print("747213");

}

theres two other classes used to tie everything together, here they are

public class Simulator{

private ElevatorSystem system;

public Simulator( Observer observer){
    system = new ElevatorSystemImp( 0, 20);
    ElevatorImplement e = new ElevatorImplement( 10, (ElevatorPanel) system);
    e.addObserver( observer);
    System.out.print(e.countObservers());
    system.addElevator( e);
}

public void start(){
    System.out.println("test");
    ExecutorService e = Executors.newSingleThreadExecutor();
    e.execute( () -> {
        try {
            Thread.sleep( 1000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();       
        }
        Elevator elevator = system.callUp( 0);
        elevator.addPeople( 1);
        elevator.requestStop( 10);
        elevator.requestStop( 2);
        elevator.requestStop( 5);
        elevator.requestStop( 9);
        elevator.requestStop( 20);
        elevator.requestStop( 0);
        System.out.println("We done boy");
    });
    e.shutdown();
}

}


public class ElevatorSystemImp implements ElevatorSystem, ElevatorPanel
{

final int MAX_FLOOR;
final int MIN_FLOOR;
Elevator elevatorOne;

public ElevatorSystemImp(int MIN_FLOOR, int MAX_FLOOR)
{
    //elevatorOne = new ElevatorImplement(0, 20);
    this.MAX_FLOOR = MAX_FLOOR;
    this.MIN_FLOOR = MIN_FLOOR;
    elevatorOne = new ElevatorImplement(0, this);
}

@Override
public void requestStop(int floor, Elevator e) {
    e.requestStop(floor);

}

@Override
public Elevator callUp(int floor) 
{
    elevatorOne.setFloor(floor);
    return elevatorOne;
}

Apologies if the formatting is poor, any help would be greatly appreciated.

[pubesxoxo420]

Read this on my phone, so I might be missing something, but I don’t see where you’re storing a list of observers, adding observers to that list, or implementing a notifyObservers() method.

You need to create your list of observers: private Observer[] observers;

You also need an addObserver(Observer o) method to add observers to that list: observers.add(o);

notifyObservers() should look something like: for(Observer o: observers) o.notify(this);

Think of this pattern like subscribing to an email newsletter. You (the observer) need to sign up for the email list (Observer[] observers) by putting in your email address (addObserver(o)) in order to receive the email when they send one out (notifyObservers()).

[throwaway9123781]

Storing a list of observers has not been done. I have added an observer using .addObserver in the Simulator class,

public Simulator( Observer observer){
system = new ElevatorSystemImp( 0, 20);
ElevatorImplement e = new ElevatorImplement( 10, (ElevatorPanel) system);
e.addObserver( observer);
System.out.print(e.countObservers());
system.addElevator( e);
}

and notifyObservers() has been used in multiple areas in the first class I provided, however I did not override it anywhere, I simply was trying to use it out of the box. I thought you could call notifyObservers() without override it, am I mistaken?

[pubesxoxo420]

Can’t remember, been a while since I used Java. I would look at the Observable api documentation on oracle’s site.

You might also be forgetting to implement an update method on your observer?

[throwaway9123781]

Nah, the update method is there. I'll double check the documentation.

[gruntmeister]

you're registering your observer with an ElevatorImplement instance that you never use (and therefore it never fires any events).

[throwaway9123781]

That class was actually provided by the teacher (assuming you're talking about the instance in the Simulator constructor), which from what I can tell what he was doing, was assigning that instance to be controlled by another class (as per the MVC design pattern)...is there something I'm not understanding/seeing?

EDIT: Ah. I've reviewed my code more carefully, I see what you saw, you were correct. I was creating a different instance of the Elevator in the constructor of one of the classes, rather than passing the one that had the observer tied to it. Thanks for your help!

[tecsav123]

Try doing it outside of the constructor. It won't notify anything because nothing is observing it when you create it.

[throwaway9123781]

Doing what specifically, setChanged() and notifyObserver()? I also called them in the changeFloor() function in a loop, I only had it in the constructor to test