Using interface methods of enum in method accepting class

ayushgp :

I have a method that needs to accept a Enum class. These enums implement an interface. Now I need access to both Enum methods like ordinal(), name(), etc and my interface methods. What I've tried:

public <T extends ConfigFeature, Enum> void showEnabledFeatures(Class<T> enumType, long mask) {
    List<T> list = Arrays.asList(enumType.getEnumConstants());
    list.forEach(item -> {
        // My interface's method, works fine
        item.getMask();
        // Enum method doesn't work:
        // item.ordinal();
    });
}

Reversing the order reverses the working:

public <T extends Enum, ConfigFeature> void showEnabledFeatures(Class<T> enumType, long mask) {
    List<T> list = Arrays.asList(enumType.getEnumConstants());
    list.forEach(item -> {
        // My interface's method, doesn't work now
        // item.getMask();
        // Enum method now works:
        item.ordinal();
    });
}

Is there a way to get access to both methods from interface and Enum?

Sweeper :

You are using the wrong syntax to say that T must implement this interface AND is an enum.

This:

<T extends ConfigFeature, Enum>

is not constraining T to Enum, but actually creating a new generic parameter called Enum.

Similarly,

<T extends Enum, ConfigFeature>

is not constraining T to ConfigFeature. You are declaring a new generic parameter called ConfigFeature.

The correct syntax is to use &:

<T extends Enum<T> & ConfigFeature>

Note that the order is actually important here! Enum can only come first.

According to here, only the first constraint can be a class, and then the ones after it must all be interfaces:

TypeParameter:
    {TypeParameterModifier} Identifier [TypeBound]

TypeParameterModifier:
    Annotation

TypeBound:
    extends TypeVariable
    extends ClassOrInterfaceType {AdditionalBound}

AdditionalBound:
    & InterfaceType