Map集合遍历方法

      Map<String,String> map = new HashMap<String, String>();
      map.put("1", "a1");
      map.put("2", "a2");
      map.put("3", "a3");
      //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 +" value: "+ map.get(key));
   }
      //第二种：推荐，特别是遍历大容量时
      for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println("key: " + entry.getKey() +" value: "+ entry.getValue());
   }
     
      //第三种：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() +" value: "+ entry.getValue());
   }