Annotations for Java enum singleton

[moon]

As Bloch states in Item 3 ("Enforce the singleton property with a private constructor or an enum type") of Effective Java 2nd Edition, a single-element enum type is the best way to implement a singleton. Unfortunately the old private constructor pattern is still very widespread and entrenched, to the point that many developers don't understand what I'm doing when I create enum singletons.A simple \[code\]// Enum Singleton\[/code\] comment above the class declaration helps, but it still leaves open the possibility that another programmer could come along later and add a second constant to the enum, breaking the singleton property. For all the problems that the private constructor approach has, in my opinion it is somewhat more self-documenting than an enum singleton.I think what I need is an annotation which both states that the enum type is a singleton and ensures at compile-time that only one constant is ever added to the enum. Something like this:\[code\]@EnumSingleton // Annotation complains if > 1 enum element on EnumSingletonpublic enum EnumSingleton { INSTANCE;}\[/code\]Has anyone run across such an annotation for standard Java in public libraries anywhere? Or is what I'm asking for impossible under Java's current annotation system?