仅具有一个实例的类，该实例可从所有其他类访问

Question

I need to create a class that contains a lot of information (slow to initialize). I am trying to access this class from my other classes. This class should only be created once because it is slow to load and takes a lot of memory. My only idea of how to do this is to create an instance of the class in the loader class and then pass it from class to class as I switch through them.

I feel like there is a better way to do this. I thought about making all the methods and variables in this class static but then I would still have to make a new object in each new class which I think would then re-initialize the object(which I don't want to do).

I am not sure if there is a better way to do this... thoughts?

Answer 1

What you are asking for is a singleton. The easiest way of doing this is using an enum instance - this is the simplest way to takes care of thread-safety issues that can arise when you try to use static members.

That said, singletons are generally considered to be a sign of an architecture problem. This is a general rule, and you may very well have good reasons for doing it this way - just make sure that your reasons are valid. The singleton anti-pattern tends to create strong coupling between different layers of the application, leading to fragile, difficult to test code.

As an alternative, if dependency injection is an option for you, then construct your object once and inject it where needed. Note that you don't have to have a DI framework to use dependency injection (you can just pass the object in to the constructors of the dependent objects). This allows you to be hyper-aware of the locations where that singleton is actually used.