Java如何遍历Map的所有的元素

JDK1.4中

Map map = new HashMap();

    Iterator it = map.entrySet().iterator();

    while (it.hasNext()) {

        Map.Entry entry = (Map.Entry) it.next();

        Object key = entry.getKey();

        Object value = entry.getValue();

}

JDK1.5中,应用新特性For-Each循环

Map m = 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>();

  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

 //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));

   }

 

      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();      }          //遍历  

   

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));

   }

}