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>();

   //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());
}

   Map.Entry 也可以写成Entry。  

   // 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();   
} //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));
   }
}