JAVA遍历map元素

第一种：

Map map = new HashMap();
Iterator iter = map.entrySet().iterator();
while (iter.hasNext()) {
    Map.Entry entry = (Map.Entry) iter.next();
    Object key = entry.getKey();
    Object val = entry.getValue();
}

 效率高,推荐使用此种方式！

第二种：

Map map = new HashMap();
Iterator iter = map.keySet().iterator();
while (iter.hasNext()) {
    Object key = iter.next();
    Object val = map.get(key);
}

 效率低,以后尽量少使用！

JDK1.5中,应用新特性For-Each循环

Map map = new HashMap();
for(Object o : map.keySet()){
    map.get(o);
}

返回的 set 中的每个元素都是一个 Map.Entry 类型。

private Hashtable<String, String> emails = new Hashtable<String, String>();
   //方法一: 用entrySet()
   Iterator it = emails.entrySet().iterator();
   while(it.hasNext()){
       Map.Entry m=(Map.Entry)it.next();
       logger.info("email-" + m.getKey() + ":" + m.getValue());
   }

   // 方法二：jdk1.5支持，用entrySet()和For-Each循环()
   for (Map.Entry<String, String> m : emails.entrySet()) {
       logger.info("email-" + m.getKey() + ":" + m.getValue());
   }

   // 方法三：用keySet()
   Iterator it = emails.keySet().iterator();
   while (it.hasNext()){
       String key;
       key=(String)it.next();
       logger.info("email-" + key + ":" + emails.get(key));
   }

// 方法五：jdk1.5支持，用keySEt()和For-Each循环

for(Object m: emails.keySet()){
       logger.info("email-" + m+ ":" + emails.get(m));
   }

 

另外 我们可以先把hashMap 转为集合Collection，再迭代输出，不过得到的对象

 Map    aa    =    new    HashMap();
 aa.put("tmp1",    new    Object());      //追加      替换用同样的函数.
 aa.remove("temp1");                        //删除
 for    (Iterator    i    =    aa.values().iterator();    i.hasNext();    )
{
         Object    temp    =    i.next();
 }

 

来个完整的，包含TreeSet的元素内部排序的

public static void main(String[] args) {
   ArrayList<String> list = new ArrayList<String>();
   HashMap<Object,Object> hash = new HashMap<Object,Object>();
   TreeMap<Object,Object> treeMap = new TreeMap<Object,Object>();
   list.add("a");
   list.add("b");
   list.add("c");

   hash.put(3, 3);
   hash.put(4, 4);
   hash.put(5, 5);
   hash.put(6, 6);
   hash.put(1, 1);
   hash.put(2, 2);

   treeMap.put(1, 1);
   treeMap.put(2, 2);
   treeMap.put(3, 3);
   treeMap.put(4, 4);
   treeMap.put(5, 5);
   treeMap.put(6, 6);

   //list遍历
   for(String m: list){
    System.out.println(m);
   }
   // hashmap entrySet() 遍历
   for(Map.Entry<Object,Object> m: hash.entrySet()){
    System.out.println(m.getKey()+"---"+m.getValue());
   }
   //hashmap keySet() 遍历
   for(Object m: hash.keySet()){
    System.out.println(m+"---"+hash.get(m));
   }
   // treemap keySet()遍历
   for(Object m: treeMap.keySet()){
    System.out.println(m+"---"+treeMap.get(m));
   }
}