定义设计一个大学的类系统。学校中有学生、教师和职员，每种人员都有自己的特性，他们之间又有相同的地方。试利用继承机制定义这个系统中的各个类及类上必需的操作。-The definition of a university class system design. Schools, students, teachers and staff, each of whom have their own characteristics, among them have the same place. Try