Question

I am trying to call a method which takes a list of Interface with a list of Enum (which implements Interface). This gives the following compile error:

The method method(List<Interface>) in the type Class is not applicable for the arguments (List<Enum>)

This is the interface:

public interface Interface {
}

This is the enum that implements the interface:

public enum Enum implements Interface {
}

This is the calling class:

import java.util.ArrayList;
import java.util.List;

public class Class {
    public static void method(List<Interface> list){
    }

    public static void main(String[] args) {
        List <Enum> enumList = new ArrayList<Enum>();
        method(enumList); //This line gives the compile error.
    }
}

Why is there a compile error? To me it seems that it should work because the Enum implements that interface.

Answer 1

This is because even is Car extends Vehicle, List<Car> does not extend List<Vehicle>. If it did, you could do the following:

List<Car> listOfCars = new ArrayList<Car>();
List<Vehicle> listOfVehicles = listOfCars;
listOfVehicles.add(new Bicycle());
// and now the list of cars contains a bicycle: not pretty.