Can I extend a class and override enclosed enum type?

Question

If I have a class that contains an enum type, can I extend this class and override the enum type or add more constants to this enum? The purpose is that user will b

Answer 1

You can't extend enum. enums are essentially a final class. However, enums can implement, so combined with generics, you get:

interface Color{

}
enum CarColor implements Color{
    BLUE,
    GREEN;
}
enum RacingCarColor implements Color{
    BLUE,
    GREEN,
    YELLOW;
}
class Vehicle {
    protected T color;
    protected Vehicle(T color){
        this.color = color;
    }
    public T getColor(){
        return color;
    }
}

class Car extends Vehicle{ 
    public Car(CarColor color){
        super(color);
    }
}

class RacingCar extends Vehicle{ 
    public RacingCar(RacingCarColor color){
        super(color);
    }
}

Voila!

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If you want to require that the type be a Color and be an enum, use this bound:

class Vehicle & Color> { ...

Or a curious equivalent:

class Vehicle> { ...