为什么不能强制转换

package course;

public class Course {

public String id;

public String name;

public Course(String id,String name)

{

this.id=id;

this.name=name;

}

}

package course;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

//选课类就是一个List容器

public class ChooseCourse {

public List choose;

public ChooseCourse()

{

this.choose=new ArrayList();

}

public void add()

{

Course cr=new Course("1.","数据库");

Course[]cr2={new Course("2.","操作系统"),new Course("3.","计算机网络")}; 

choose.add(cr);

choose.add(1, cr2);

Course cr3=(Course) choose.get(0);

System.out.println("添加了课程"+cr3.id+cr3.name);

}

public void iterator()

{

Iterator it=choose.iterator();

while(it.hasNext())

{

Course cr=(Course) it.next();

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

}

}

public static void main(String[] args) {

ChooseCourse cc=new ChooseCourse();

cc.add();

cc.iterator();

// TODO 自动生成的方法存根

}

}

错误信息xception in thread "main" java.lang.ClassCastException: [Lcourse.Course; cannot be cast to course.Course。。

请问哪里错了