JavaFx 8 Slider

I need a help about taking 2 sliders value and pass it to a function in order to calculate BMI
For ex:
height.valueProperty().addListener(new ChangeListener<Number>() {
public void changed(ObservableValue<? extends Number> ov,
Number old_val, Number new_val2) {
// System.out.println(new_val.doubleValue());
heightValue.setText(String.format("%.2f", new_val2));
}
});
weight.valueProperty().addListener(new ChangeListener<Number>() {
public void changed(ObservableValue<? extends Number> ov,
Number old_val, Number new_val) {
// System.out.println(new_val.doubleValue());
weightValue.setText(String.format("%.2f", new_val));


}
});

I try to pass these new_val2 and new_val to the function

public double calculateBMI(double a,double b)

Thanx