Innerclass exercise 18 finished

Exercise 18: (1) Create a class containing a nested class. In main( ), create an instance
of the nested class.
* This is use nested class of inner class, don’t need a connection between the inner-class object and the outerclass object, then
you can make the inner class static
* 1. You don’t need an outer-class object in order to create an object of a nested class.
2. You can’t access a non-static outer-class object from an object of a nested class.