set是无序集合，放入set中的元素通过iterator输出时候是无序的

HashMap<String , String> hashMap = new HashMap<String , String>();
        for (int i = 0; i < 100; i++) {
            hashMap.put(i+"", i+"a");    
        }
        Set<Entry<String, String>> entry =  hashMap.entrySet(); 
        Iterator<Entry<String, String>> entryIterator = entry.iterator();
        while(entryIterator.hasNext())
        {
            Map.Entry<String, String> entryItem = entryIterator.next();
            System.out.println(entryItem.getKey()+":"+entryItem.getValue());
        }

输出结果：是乱序的

88:88a
89:89a
90:90a
91:91a
92:92a
93:93a
94:94a
95:95a
96:96a
97:97a
10:10a
98:98a
11:11a
99:99a
12:12a
13:13a
14:14a
15:15a
16:16a
17:17a
18:18a
19:19a
0:0a
1:1a
2:2a
3:3a
4:4a
5:5a
6:6a
7:7a
8:8a
9:9a
20:20a
21:21a
22:22a
23:23a
24:24a
25:25a
26:26a

1.hashmap遍历方法：

Set ss=hm.entrySet() ;//返回Map.Entry 接口实现

printElements(ss); //输出键值对利用迭代器

Iterator i=ss.iterator() ;   //通过 Map.Entry静态接口获取元素
    while(i.hasNext())
    {
    Map.Entry me=(Map.Entry)i.next() ;//强制转换
    System.out.println(me.getKey()+":"+me.getValue());

    }