How can I implement @Singleton annotation?

Question

Possibly a repeated question. But I need to implement something like

@Singleton public class Person { } 

That will ensure only single instance of Person object.

One way is to make constructor private. But that makes the Singleton annotation redundant.

I could not really understand if I can really restrict object creation to single object without making the constructor private.

Is that even possible?

Answer 1

No annotation can prevent a class from being instantiated. However, if you plan to implement something like a Dependency Injection framework, or just a simple object factory, then you can use reflection to read the annotation and prevent the class from being instantiated more than once, but I understand this is not the answer you were looking for.

You can actually think about dropping the singleton pattern and moving to some more modern solution like a proper DI framework, which can give you the same result - with more flexibility.