Java：如何在枚举中的类类型字段上设置界限

Question

I have an enum which has a property that is another class. I want to somewhere put a constraint that all instances of the enum have should have a value for that property that extend a certain upper bound, in this case an interface. Here is the basic working example without the bound:

public enum MyClassRegistry
{
    MyClass(1,com.example.MyClass.class)

    private int typeId;
    private Class theClass;
}

What I want to do next is something like:

public enum MyClassRegistry 
{
    MyClass(1,com.example.MyClass.class)

    private int typeId;
    private Class<T extends SomeInterface> theClass;
}

To enforce that all values of this field extend a certain upper bound. Is this possible? If so, what is the syntax for this?

Answer 1

public enum MyClassRegistry
{
    MyClass(1,com.example.MyClass);

    private int typeId;
    private Class<? extends SomeInterface> theClass;

    MyClassRegistry(int typeId, Class<? extends SomeInterface> theClass) {
        this.typeId = typeId;
        this.theClass = theClass;
    }
}

Answer 2

An enum type cannot declare any generic type parameters.

If you mean you want to have a field that has a type of some super type, an interface for example, simply declare the field as having that type.

public enum MyClassRegistry
{
    First(1, new InterfaceFirstImpl()),
    Second(2, new InterfaceSecondImpl()) ;

    MyClassRegistry (int id, Interface value) {
        this.typeId = id;
        this.value = value;
    }
    private int typeId;
    private Interface value;
}