If I have a superclass, let's call it Car, with the constructor parameters String name, String color, double wheelSize, and a subclass of this, let's call it Truck, with the constructor parameters String name, String color, double wheelSize, and double truckBedArea, and in the subclass (Truck), I have a method called modifyCar with the paramaters Car car, String newName, String newColor, double newWheelSize, and double newTruckBedArea, how can I find a way to take that Car object and specify that it is indeed a Truck, so I can then use a Truck setter (setTruckBedArea) to set the new truck bed area? This example isn't a great comparison to my actual assignment, but I have an ArrayList field of my superclass (Cars) called "ArrayList cars" of "Car" objects, and I need to find a way to change that "Car" object in this ArrayList field, which I have already found a way of doing. I simply loop through each item in the ArrayList of "Cars" until it equals the instance of the Car put in as a parameter, and if it does, I then say "cars.get(i).//setter" (essentially). However, it would not work if I say "cars.get(i).setTruckBedArea(newTruckBedArea)". I am not sure how to cast the Car object within this list of Cars to a Truck specifically, so I can then access the setter I want to use. The main issue is that I am required to implement an interface (let's call it "Vehicle") wherein the ArrayList cars has to be of type cars, since it is specified to be that in the Vehicle interface (otherwise I would just change the ArrayList field to be ArrayList trucks).

Example:

public class Truck implements Vehicle { //have to implement this interface
    //... other fields
    private ArrayList<Car> cars;
    //... other methods/constructors
    public void modifyCar(Car car, String newName, String newColor, double newWheelSize, double newTruckBedArea) { 
//have to have "Car car" as parameter for this method because of interface
        for (int i = 0; i < cars.size(); i  ) {
            if (cars.get(i).equals(car)) {
                cars.get(i).setColor(newColor);
                cars.get(i).setName(newName);
                cars.get(i).setWheelSize(newWheelSize);
                cars.get(i).setTruckBedArea(newTruckBedArea); //will produce error
            }
        }
    }
}

CodePudding user response：

As far as I understand the question, you can use "instanceof" operator:

   if(cars.get(i) instanceof Truck){
       Truck truck = (Truck) cars.get(i);
       truck.setTruckBedArea(newTruckBedArea);
   }

instanceof operator returns a boolean value in result of whether an object is an instance of given type or not.

CodePudding user response：

Vehicle should be an Abstract class.

Car Interface

public interface Car {
    void modifyCar(Car car, String newName, String newColor, double newWheelSize, double newTruckBedArea);
}

Vehicle Abstract Class

public abstract class Vehicle implements Car {

    String name;
    String color;
    double wheelSize;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public double getWheelSize() {
        return wheelSize;
    }

    public void setWheelSize(double wheelSize) {
        this.wheelSize = wheelSize;
    }

}

Truck Class

public class Truck extends Vehicle {

    double truckBedArea;
    private ArrayList<Car> cars;

    public double getTruckBedArea() {
        return truckBedArea;
    }

    public void setTruckBedArea(double truckBedArea) {
        this.truckBedArea = truckBedArea;
    }

    public ArrayList<Car> getCars() {
        return cars;
    }

    public void setCars(ArrayList<Car> cars) {
        this.cars = cars;
    }

    @Override
    public void modifyCar(Car car, String newName, String newColor, double newWheelSize, double newTruckBedArea) {
        for (int i = 0; i < cars.size(); i  ) {
            if (cars.get(i).equals(car)){
                ((Vehicle)cars.get(i)).setColor(newColor);
                ((Vehicle)cars.get(i)).setWheelSize(newWheelSize);
                ((Truck)cars.get(i)).setTruckBedArea(newTruckBedArea);
            }
        }
    }

}

Run code.

public static void main(String[] args) {
        // TODO code application logic here
        Truck trucks = new Truck();
        trucks.setColor("Red");
        trucks.setName("Nissan");
        trucks.setWheelSize(20.15);
        trucks.setTruckBedArea(3.5);
        ArrayList<Car> cars = new ArrayList<Car>();
        cars.add(trucks);
        trucks.setCars(cars);
        
        trucks.modifyCar(trucks, "Kia", "Blue", 15.5, 14.0);

        System.out.println(trucks.getTruckBedArea());
    }