代码没问题啊，为什么我运行的时候出错了

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.Scanner;

public class SetTest {

public List<Course> coursesToSelect;

public SetTest(){

coursesToSelect=new ArrayList<Course>();

}

public void testAdd(){

Course cr1=new Course("1","数据结构");

coursesToSelect.add(cr1);

Course temp=(Course) coursesToSelect.get(0);

// System.out.println("添加了课程："+temp.id+":"+temp.name);

Course cr2=new Course("2","C语言");

coursesToSelect.add(0, cr2);

Course temp2=(Course) coursesToSelect.get(0);

// System.out.println("添加了课程："+temp2.id+":"+temp2.name);

// coursesToSelect.add(cr1);

// Course temp0=(Course) coursesToSelect.get(2);

// System.out.println("添加了课程："+temp.id+":"+temp.name);

Course[] course={new Course("3","离散数学"),new Course("4","汇编语言")};

coursesToSelect.addAll(Arrays.asList(course));

Course temp3=(Course) coursesToSelect.get(3);

Course temp4=(Course) coursesToSelect.get(4);

// System.out.println("添加了两门课程："+temp3.id+":"+

// temp3.name+";"+temp4.id+":"+temp4.name);

Course[] course2={new Course("5","高等数学"),new Course("6","大学英语")};

coursesToSelect.addAll(2, Arrays.asList(course2));

Course temp5=(Course) coursesToSelect.get(2);

Course temp6=(Course) coursesToSelect.get(3);

// System.out.println("添加了两门课程："+temp5.id+":"+

// temp5.name+";"+temp6.id+":"+temp6.name);

}

public void testForEach(){

System.out.println("有如下课程待选(通过for each访问)：");

for(Object obj:coursesToSelect){

Course cr=(Course) obj;

System.out.println("课程:"+cr.id+":"+cr.name);

}

}

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

SetTest st=new SetTest();

st.testAdd();

st.testForEach();

//创建一个学生对象

Student student=new Student("1","小明");

System.out.println("欢迎学生："+student.name+"选课！");

//创建一个Scanner对象，用来接收从键盘输入的课程ID

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:st.coursesToSelect){

if(cr.id.equals(courseid)){

student.courses.add(cr);

}

}

}

// //打印输出学生所选的课程

// for (Course cr : student.courses) {

// System.out.println("选择了课程:"+cr.id+":"+cr.name);

// }

st.testForEachForSet(student);

}

public void testForEachForSet(Student student){

for (Course cr : student.courses) {

System.out.println("选择了课程:"+cr.id+":"+cr.name);

}

}

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