The Singleton pattern has several advantages over static classes.

1. First, a singleton can extend classes and implement interfaces, while a static class cannot (it can extend classes, but it does not inherit their instance members).
2. A singleton allows access to a single created instance – that instance (or rather, a reference to that instance) can be passed as a parameter to other methods, and treated as a normal object. A static class allows only static methods.
3. Singleton objects are stored in Heap, but static objects are stored in stack.
4. We can clone (if the designer did not disallow it) the singleton object, but we can not clone the static class object .
5. Singleton classes follow the OOP (object oriented principles), static classes do not.
6. We can implement an interface with a Singleton class, but a class’s static methods (or e.g. a C# static class) cannot.