Hi Ming Yu,
For this case, we won't find any difference in static method and normal(Instance) method based on variable.
But basic difference in calling the method.
Static Method
To call static method, it is not required to create the object for the class. Also static method won't support polymorphism.
CLASS1=>METHOD1.
Instance Method
To call normal method(Instance), It is required to have the object for the class.
OBJ->METHOD1.
Regards
Rajkumar Narasimman