Java项目中怎么对ArrayList进行嵌套

import java.util.ArrayList;

import com.heima.bean.Person;

public class Demo5_ArrayListArrayList {
 /*
  * 集合嵌套之ArrayList嵌套ArrayList 案例:一个学校有好多班级,一个班级又有好多人;遍历输出这个学校的所有人
  */
 public static void main(String[] args) {
  ArrayList<ArrayList<Person>> school = new ArrayList<>();
  ArrayList<Person> class1 = new ArrayList<>();
  class1.add(new Person("张三", 23));
  class1.add(new Person("李四", 24));
  class1.add(new Person("王五", 25));
  ArrayList<Person> class2 = new ArrayList<>();
  class2.add(new Person("张三一", 23));
  class2.add(new Person("李四一", 24));
  class2.add(new Person("王五一", 25));
  school.add(class1);
  school.add(class2);
  for (ArrayList<Person> outer : school) {
   for (Person in : outer) {
    System.out.println(in);
   }
  }

 }

}