A static class is a class declared as a static member of another class.
1. It can access static data members of outer class even including private.
2. Static nested class cannot access non-static (instance) data member or method.
When to use nested static class in Java?
The static class is useful when the single resource is shared between all instances and generally we do this for utility classes which are required by all components and which itself doesn't have any state.
Map.Entry is the static inner class.
Java static nested class with static method
If you have the static member inside static nested class, you don't need to create instance of static nested class.