Java Array of Enum Class implementing an interface accepts other Enums not implementing Interfaces as well

I have java enums that implement a Direction interface as below.

public enum AdvanceDirection implements Direction {....}

public enum BasicDirection implements Direction {....}

I also have an enum NonDirection that doesn't implements Direction as below

public enum NonDirection {....}

I have a function that should only return an Array of Enum classes that implements Direction as below

public static <T extends Enum<T> & Direction> Class<T>[] getDirections() {
  return new Class[]{AdvanceDirection.class, BasicDirection.class, NonDirection.class};
}

But if I add NonDirection.class to this Array, it still returns it without any errors. How can I make sure that getDirections() method only returns array of Enums that implements Direction Interface ?

Usage example

public static void printDirections() {
  for (Class c: getDirections()) {
    System.out.println(c);
  }
}

You have hit a known limitation of the use of generics in Java. The language designers (sensibly IMO) decided to use type erasure to limit the impact of the introduction of generics on the runtime engine. However this limits some uses of generics that would otherwise seem natural.

Your options are:

1. use a collection instead of an array. This would be my recommendation: there's really no advantage to arrays in the case you've given and will allow tighter type checking at compile time.

2. use reflection to test the class's inheritance at runtime and throw an exception.

I realise your examples is contrived for the purpose of asking the question (for which I commend you) but the use of generics and Class objects you've shown seems quite unusual. If you give more details on what you are trying to achieve there could well be a more natural solution within Java.