java - How to instantiate a Singleton multiple times?

Question

I need a singleton in my code. I implemented it in Java and it works well. The reason I did it, is to ensure that in a mulitple environment, there is only one instance of this class.

But now I want to test my Singleton object locally with a Unit test. For this reason I need to simulate another instance of this Singleton (the object that would be from another device). So is there a possiblity to instantiate a Singleton a second time for testing purpose or do I have to mock it?

I'm not sure, but I think it could be possible by using a different class loader?

Answer 1

Traditionally, a Singleton creates its own instance, and it creates it only once. In this case it is not possible to create a second instance.

If you use Dependency Injection, you can let the framework create the singleton for you. The singleton does not guard against other instances (i.e. it has a public constructor), but the dependency injection framework instantiates only one instance. In this case, you can create more instances for testing, and your object is not cluttered with singleton code.