定义一个学生类, 需要有姓名, 年龄, 考试成绩三个成员属性. 属性(成员变量)需要私有并提供get, set方法, 可以通过构造函数进行初始化-Define a class of students, name, age, test scores three member property attributes (member variables) need to be private and get, set method, through the constructor to initial