某公司的面试题--递归拿到所有子类的id

package com;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Test1 {
	List list2 = new ArrayList();
         //构造数据库list
	public List<Student> getStudent(){
		List<Student> list = new ArrayList<Student>();
		list.add(new Student("2","1"));
		list.add(new Student("3","2"));
		list.add(new Student("4","3"));
		list.add(new Student("5","3"));
		return list;
	}
         //循环拿到所有的子类id
	public List getAll(String i,List<Student> list){

		Iterator iter = list.iterator();
		while(iter.hasNext()){
			Student student = (Student)iter.next();
			if(i.equals(student.getParentid())){
				list2.add(student.getId());
				getAll(student.getId(),list);
			}
		}
		return list2;
	}
         //测试
	public static void main(String[] args) {
		List list = new Test1().getAll("1", new Test1().getStudent());
		Iterator iter = list.iterator();
		while(iter.hasNext()){
			System.out.println((iter.next()));
		}
	}
}
     class Student {
	private String id;
	private String parentid;

	public Student() {
	}

	public Student(String id, String parentid) {
		this.id = id;
		this.parentid = parentid;
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getParentid() {
		return parentid;
	}

	public void setParentid(String parentid) {
		this.parentid = parentid;
	}
}