向map中追加元素

 public class Demo01 {

     public static void main(String[] args) {

         String mapKey = "a";
         Map<String, Map<String, Integer>> maps = new ConcurrentHashMap<String,Map<String, Integer>>();
         Map<String, Integer> map = new HashMap<String,Integer>();
         map.put("aaaa", 1);
         map.put("bbbb", 2);
         map.put("cccc", 3);

         maps.put("a", map);

         if(maps.containsKey(mapKey)){
             Map<String, Integer> tmpMap = maps.get(mapKey);
             tmpMap.put("dddd", 4);
             maps.put(mapKey, tmpMap);
         }

         //遍历maps
         Iterator<String> it = maps.keySet().iterator();
         while(it.hasNext()){
             String mapsKey = it.next();
             Map<String, Integer> mapValue = maps.get(mapsKey);
             System.out.println(mapValue);
         }
     }

 }

 输出结果：
 {bbbb=2, dddd=4, aaaa=1, cccc=3}