帮忙看看拿错了

package aaaa.imooc3;

import java.util.ArrayList;

import java.util.List;

public class ListTest {

public List coursesToSelect;

public ListTest(){

this.coursesToSelect = new ArrayList();

}

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);

}

public static void main(String args){

ListTest lt = new ListTest();

lt.testAdd();

}

}

package aaaa.imooc3;

import java.util.HashSet;

import java.util.Set;

public class Student {

public String id;

public String name;

public Set courses;

public Student(String id,String name){

this.id = id;

this.name = name;

this.courses = new HashSet();

}

}

package aaaa.imooc3;

public class Course {

public String id;

public String name;

public Course(String id,String name){

this.id = id;

this.name = name;

}

}