public static void main(String[] args) {    

   Map<String, String> map = new HashMap<String, String>();

   map.put("1", "value1");

   map.put("2", "value2");

   map.put("3", "value3");    

   // 第一种：普遍使用，二次取值

   System.out.println("通过Map.keySet遍历key和value：");

   for (String key : map.keySet()) {

    System.out.println("key= "+ key + " and value= " + map.get(key));

   }    

   //第二种

   System.out.println("通过Map.entrySet使用iterator遍历key和value：");

   Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();

   while (it.hasNext()) {

    Map.Entry<String, String> entry = it.next();

    System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());

   }    

   //第三种：推荐，尤其是容量大时

   System.out.println("通过Map.entrySet遍历key和value");

   for (Map.Entry<String, String> entry : map.entrySet()) {

    System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());

   }    

   //第四种

   System.out.println("通过Map.values()遍历所有的value，但不能遍历key");

   for (String v : map.values()) {

    System.out.println("value= " + v);

   }

  }