Q:

Why am I getting “Not on FX application thread” on JavaFX?

I am learning JavaFX and I made a demo app that has a Label detects a value change and change its display. I tried to bind the Label.textProperty to the value but stil does not work. Here is my code:
public class MainApp extends Application {

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

private Temp aTemp = new Temp();

@Override
public void start(Stage primaryStage) {

    try {
        FXMLLoader loader = new FXMLLoader(getClass().getResource("Sample.fxml"));      
        BorderPane root = (BorderPane)loader.load();
        SampleController sampleController = loader.getController();

        Scene scene = new Scene(root,600,600);
        scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());

        primaryStage.setScene(scene);
        primaryStage.show();

        sampleController.setModel(aTemp);

    } catch(Exception e) {
        e.printStackTrace();
    }
}}

And here is the model
public class Temp {
private StringProperty temp = new SimpleStringProperty("a");

private final ExecutorService service = Executors.newCachedThreadPool();

public Temp() {

    task.startConnection();
    service.submit(new Task<Integer>() {

        @Override
        public Integer call() {
            while(true) {
                try {
                    Thread.sleep(1000);
                }catch(Exception e) {
                    e.printStackTrace();
                }

                setTemp(getTemp() + "b");
                System.out.println(getTemp());

            }
        }
    });
}

public StringProperty getProperty() {
    return this.temp;
}

public String getTemp() {
    return this.temp.get();
}

public void setTemp(String value) {
    this.temp.set(value);
}

And then the controller
public class SampleController implements Initializable {

private Temp aTemp;

@FXML private Label tempLabel;

@Override
public void initialize(URL arg0, ResourceBundle arg1) {

}

public void setModel(Temp aTemp) {
    this.aTemp = aTemp;

    Platform.runLater(new Runnable() {
        @Override
        public void run() {
            tempLabel.textProperty().bind(aTemp.getProperty());
        }
    });

}}

What I got is that Label is change to "a" but wont change after and this exception: 
Exception in thread "pool-2-thread-1" 
java.lang.IllegalStateException: Not on FX application thread; currentThread = pool-2-thread-1

A:

To flesh out my comment: if you want to keep the model completely unaware of the UI, then don't bind it directly to a property of a control. Instead, on the UI side have some listener to the model property that changes the control property on the fx thread.
A code snippet (not tested, just copied and adjusted - so might not even compile ;):
public void setModel(Temp aTemp) {
    this.aTemp = aTemp;

    aTemp.tempProperty().addListener(this::updateLabelText) 

}}

private void updateLabelText() {
   Platform.runLater(() -> label.setText(aTemp.getTemp()));  
} 

