对学生管理系统进行如下修改。

(1)引入一个抽象基类Person，并将showMe方法定义为抽象方法。

(2)将类Student(本科)改为由类Person派生的类Major，并给出showMe方法的具体实现

(3)再派生一个硕士研究生类Master(硕士)和一个博士研究生类Doctor(博士) ，并通过方法覆盖实现它们各自的showMe方法

(4)分别为Major、Master、Doctor类添加至少两个新的具有不同访问权限的成员变量和对应的访问方法（类似Set和Get函数）

(5)为Student类提供比较Student, Major, Master, Doctor的对象内容是否相等的功能（要求覆盖Object类的equals方法）

-Student management system be modified as follows.

(A) introducing an abstract base class Person, and showMe method is defined as abstract methods.

(2) the class Student (undergraduate) replaced by the class Person class that derives Major, and gives the method implementation showMe

(3) and then derive a graduate class Master (MA) and a doctoral student class Doctor (PhD), and through the method overriding methods to achieve their respective showMe

(4) respectively, Major, Master, Doctor add at least two new classes have different access rights of member variables and the corresponding access method (similar to the Set and Get functions)

(5) to provide comparative Student class Student, Major, Master, Doctor of the contents of the object are equal functionality (requires override the equals method of the Object class)