createStudentAndSelectCourse里为什么不能用Student student？而要先在外面添加属性Student再在这里面用？

public void createStudentAndSelectCourse(){

    student = new Student("1","小明");
    System.out.println("欢迎学生" + student.name + "选课！");

    Scanner console = new Scanner(System.in);

    for(int i = 0;i<3;i++){
        System.out.println("请输入课程ID：");
        String courseID = console.next();
        for(Course cr:coursesToSelect){
            if(cr.id.equals(courseID)){
                student.course.add(cr);
            }
        }
    }
    for(Course cr:student.course){
        System.out.println("已选课程："+ cr.id + ":" + cr.name);
    }
}