这个是下标越界了吗？如果要改的话应该怎么改呢？
Course[] course2 = {new Course("6","计算机网络"),new Course("7","单片机原理")};
coursesToSelect.add(2, Arrays.asList(course2));
Course temp6 = (Course)coursesToSelect.get(2);
Course temp7 = (Course)coursesToSelect.get(3);
System.out.println("又添加了两门课程：" + temp6.getId() + ":" +
temp6.getName() + "\n" + temp7.getId() + ":" + temp7.getName());
