学生选课--判断Set中课程是否存在章节举例代码的Course类型不一致问题，应该用Set 类型并用HashSet初始化才准确吧？
public Set<Course> coursesToSelect; public Student student;
/**
* 学生类
* @author Administrator
*
*/
public class Student {
public String id;
public String name;
public Set<Course> courses;
public Student(String id, String name) {
this.id = id;
this.name = name;
this.courses = new HashSet<>();
}
}
