导入了包，里边方法错误，打出来还没有提示希望访问，报错

Question

package com.imooc.collection;import java.util.ArrayList;import java.util.Arrays;import java.util.List; public class ListTest { /** * 用于存放备选课程List */ public List coursesToSelect;//课程属性 public ListTest(){ this.coursesToSelect=new ArrayList(); } /**  * 用于往coursesToSelect中添加备选课程  */  public void testAdd(){  //创建一个课程对象，并通过调用add方法，添加到备选课程中list去  Course cr1=new Course("1","数据类型");  coursesToSelect.add(cr1);  Course temp=(Course) coursesToSelect.get(0);//这是看是否插入进去了，提出来的用get方法  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);  //存入忽略原来类型只当是object,取出也是object,所以要强转成课程类型   System.out.println("添加了课程"+temp2.id+":"+temp2.name);   //这次是用数组的方法添加，再把数组转化成列表，的addall方式   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);  public static void main(String[] args) { ListTest It=new ListTest(); It.testAdd();}}