跟老师一样敲的。但是我是顺序输出。我用的是MyEclipse。不是set是随机吗。我试了至少4次不一样的东西了都是顺序

package com.imooc.collection;

import java.util.HashMap;

import java.util.Map;

import java.util.Scanner;

import java.util.Set;

public class MapTest {

public Map<String,Student>students;

public MapTest() {

this.students=new HashMap<String,Student>();

}

public void testPut() {

Scanner console=new Scanner(System.in);

int i=0;

while(i<3) {

System.out.println("请输出学生ID：");

String ID=console.next();

Student st=students.get(ID);

if(st==null) {

System.out.println("请输入学生姓名：");

String name=console.next();

Student newStudent=new Student(ID,name);

students.put(ID, newStudent);

System.out.println("成功添加学生："+students.get(ID).name);

i++;

}else {

System.out.println("该学生ID已被占用");

}

}

}

public void testKeySet() {

Set<String>keySet=students.keySet();

for(String stuId:keySet) {

Student st=students.get(stuId);

if(st!=null)

System.out.println("学生："+st.name);

}

}

public static void main(String[] args) {

// TODO Auto-generated method stub

MapTest mt=new MapTest();

mt.testPut();

mt.testKeySet();

}

}