Ich versuche, mein erstes Factory Design Pattern zu implementieren, und ich bin mir nicht sicher, wie ich die Verwendung von instanceof vermeiden soll, wenn ich die werksseitig erstellten Objekte zu Listen hinzufüge. Das versuche ich zu tun:

for (ABluePrint bp : bluePrints) {
    AVehicle v = AVehicleFactory.buildVehicle(bp);
    allVehicles.add(v);

    // Can I accomplish this without using 'instanceof'?
    if (v instanceof ACar) {
        cars.add((ACar) v);
    } else if (v instanceof ABoat) {
        boats.add((ABoat) v);
    } else if (v instanceof APlane) {
        planes.add((APlane) v);
    }
}

Von dem, was ich auf SO gelesen habe, ist die Verwendung von 'instanceof' ein Codegeruch. Gibt es eine bessere Möglichkeit, den vom Werk erstellten Fahrzeugtyp zu überprüfen, ohne 'instanceof' zu verwenden?

Ich freue mich über Feedback / Vorschläge zu meiner Implementierung, da ich nicht einmal sicher bin, ob ich das richtig mache.

Vollständiges Beispiel unten:

import java.util.ArrayList;

class VehicleManager {

    public static void main(String[] args) {

        ArrayList<ABluePrint> bluePrints = new ArrayList<ABluePrint>();
        ArrayList<AVehicle> allVehicles = new ArrayList<AVehicle>();
        ArrayList<ACar> cars = new ArrayList<ACar>();
        ArrayList<ABoat> boats = new ArrayList<ABoat>();
        ArrayList<APlane> planes = new ArrayList<APlane>();

        /*
        *  In my application I have to access the blueprints through an API
        *  b/c they have already been created and stored in a data file.
        *  I'm creating them here just for example.
        */
        ABluePrint bp0 = new ABluePrint(0);
        ABluePrint bp1 = new ABluePrint(1);
        ABluePrint bp2 = new ABluePrint(2);
        bluePrints.add(bp0);
        bluePrints.add(bp1);
        bluePrints.add(bp2);

        for (ABluePrint bp : bluePrints) {
            AVehicle v = AVehicleFactory.buildVehicle(bp);
            allVehicles.add(v);

            // Can I accomplish this without using 'instanceof'?
            if (v instanceof ACar) {
                cars.add((ACar) v);
            } else if (v instanceof ABoat) {
                boats.add((ABoat) v);
            } else if (v instanceof APlane) {
                planes.add((APlane) v);
            }
        }

        System.out.println("All Vehicles:");
        for (AVehicle v : allVehicles) {
            System.out.println("Vehicle: " + v + ", maxSpeed: " + v.maxSpeed);
        }

        System.out.println("Cars:");
        for (ACar c : cars) {
            System.out.println("Car: " + c + ", numCylinders: " + c.numCylinders);
        }

        System.out.println("Boats:");
        for (ABoat b : boats) {
            System.out.println("Boat: " + b + ", numRudders: " + b.numRudders);
        }

        System.out.println("Planes:");
        for (APlane p : planes) {
            System.out.println("Plane: " + p + ", numPropellers: " + p.numPropellers);
        }
    }
}

class AVehicle {

    double maxSpeed;

    AVehicle(double maxSpeed) {
        this.maxSpeed = maxSpeed;
    }
}

class ACar extends AVehicle {

    int numCylinders;

    ACar(double maxSpeed, int numCylinders) {
        super(maxSpeed);
        this.numCylinders = numCylinders;
    }
}

class ABoat extends AVehicle {

    int numRudders;

    ABoat(double maxSpeed, int numRudders) {
        super(maxSpeed);
        this.numRudders = numRudders;
    }
}

class APlane extends AVehicle {

    int numPropellers;

    APlane(double maxSpeed, int numPropellers) {
        super(maxSpeed);
        this.numPropellers = numPropellers;
    }
}

class AVehicleFactory {

    public static AVehicle buildVehicle(ABluePrint blueprint) {

        switch (blueprint.type) {

            case 0:
                return new ACar(100.0, 4);

            case 1:
                return new ABoat(65.0, 1);

            case 2:
                return new APlane(600.0, 2);

            default:
                return new AVehicle(0.0);
        }
    }
}

class ABluePrint {

    int type; // 0 = car; // 1 = boat; // 2 = plane;

    ABluePrint(int type) {
        this.type = type;
    }
}