Java: generic enum in method parameter

Question

Correspondig the following question:

Java: Enum parameter in method

I would like to know, how can I format the code to require enums generically.

Foo.java

public enum Foo {      a(1), b(2); } 

Bar.java

public class Bar {     public Bar(generic enum); } 

Later on I'll have more enum classes like "foo", but you can still create bar containing any kind of enum class. I have "jdk1.6.0_20" by the way...

Answer 1

See the methods in EnumSet for reference, e.g.

public static <E extends Enum<E>> EnumSet<E> of(E e) 

(This method returns an EnumSet with one element from a given Enum element e)

So the generic bounds you need are: <E extends Enum<E>>

---

Actually, you will probably make Bar itself generic:

public class Bar<E extends Enum<E>> {      private final E item;      public E getItem(){         return item;     }      public Bar(final E item){         this.item = item;     } } 

You may also add a factory method like from, with etc.

public static <E2 extends Enum<E2>> Bar<E2> with(E2 item){     return new Bar<E2>(item); } 

That way, in client code you only have to write the generic signature once:

// e.g. this simple version Bar<MyEnum> bar = Bar.with(MyEnum.SOME_INSTANCE); // instead of the more verbose version: Bar<MyEnum> bar = new Bar<MyEnum>(MyEnum.SOME_INSTANCE); 

Reference:

• Java Tutorial - Learning the Java Language
  • Classes and Objects > Enum Types
  • Generics