Generics using Enum in Java

enums are final types, which means, you can not extend from them

a generic like wants a Class as Parameter which is Days or an extended class, but the extended class is not possible

so the only parameter possible is Days and you don't need a generic, if only one value is possible

You cannot extend enums in java (http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html towards the end). Thus is not possible.

-IF you need your class to work only with your enum you don't need generics

-if instead you need it to work with others enum (does it makes sense?) you don't need to specify the extend.

What does exactly your State class do ?

Don't use a generics bound. There's no need. Just use an unbounded type, like this:

public class State<T> {
    public State(T startState) {
        // whatever
    } 
}

And to use it:

State<Days> dayState = new State<Days>(Days.SUNDAY);

This is a straightforward typed class that doesn't need a bound.

The only bound that might make sense is a bound to an enum:

public class State<T extends Enum<T>> {
    public State(T startState) {
        // whatever
    } 
} 

This version requires that the generic parameter be an enum. With this version the above usage example would still compile, but this would not compile (for example):

State<String> dayState = new State<String>("hello");

because String is not an enum.