Question

Is there a clean way of passing an enumeration CLASS to a function?

Consider something like this:

public enum MyEnum implements XYZ {

   //enum values
   A,
   B,
   C;
}

public void getEnumeration(final Class<? extends XYZ> myEnum) {

   //go through enumeration
   for (XYZ xyz : myEnum.getEnumConstants()
       System.out.println(xyz.toString());
}

enumeration passed in as follows:

getFunction(MyEnum.class);

now… the above works and I can pass my enumeration to the getEnumeration() function just fine. HOWEVER, I’d like to ensure that what I am passing in is indeed an enumeration and not any class that implements XYZ. I realize that enumeration is a type of class, but is there a way to strong type this such that the compiler would pick it up if I pass in a class that implement XYZ instead of enumeration that implements XYZ?

Answer 1

You can do this:

public static <T extends Enum<T> & XYZ> void getEnumeration(Class<T> myEnum) {
    // ...
}

Here’s an actual example I wrote to test out my concept:

public class EnumTest {
    public enum Runnables implements Runnable {
        HELLO {
            @Override
            public void run() {
                System.out.print("Hello, ");
            }
        },
        WORLD {
            @Override
            public void run() {
                System.out.println("world!");
            }
        };
    }

    public static <T extends Enum<T> & Runnable> void getEnumeration(Class<T> myEnum) {
        for (Runnable runnable : myEnum.getEnumConstants())
            runnable.run();
    }

    public static void main(String[] args) {
        getEnumeration(Runnables.class);
    }
}