HashMap的迭代器有关问题，小郁闷

import java.util.*;import java.util.Map.Entry;//为何这里已经导入util.*了，还必须导入util.Map.Entry？public class T6 {    public static void main(String[] args) {        HashMap<String, String> hm = new HashMap<String, String>();        String email = "lily@sohu.com,tom@163.com,rock@sina.com";        String[] ss = email.split(",");        for (String str : ss) {            String name = str.substring(0, str.indexOf("@"));            String url = str.substring(str.indexOf("@") + 1);            hm.put(name, url);        } //上边这一部分可以不看，关键是下边的迭代器部分，为何写成上边这种情况，运行时会输出第一个结果lily 163.com// 然后抛出如下异常 Exception in thread "main" java.util.NoSuchElementException//    at java.util.HashMap$HashIterator.nextEntry(HashMap.java:796)//    at java.util.HashMap$EntryIterator.next(HashMap.java:834)//    at java.util.HashMap$EntryIterator.next(HashMap.java:832)//    at t6.T6.main(T6.java:20)//        Iterator<Entry<String, String>> it = hm.entrySet().iterator();//        while (it.hasNext()) {////            System.out.println(it.next().getKey() + " " + it.next().getValue());//        }//但是写成下面的却没有问题            Iterator<Entry<String, String>> it = hm.entrySet().iterator();        while (it.hasNext()) {            Entry<String, String> entry = it.next();            System.out.println(entry.getKey() + " " + entry.getValue());        }    }}