code: public Object put(Object key,Object subKey,Object value){
          HashMap a = (HashMap)super.get(key);
          if(a==null){
              a = new HashMap();
              super.put(key,a);
          }
          return a.put(subKey,value);
      }
docs: Associates the specified value with the specified key and subKey in this map.
  If the map previously contained a mapping for this key and subKey , the old value is replaced.
  @param key Is a Primary key.
  @param subKey  with which the specified value is to be associated.
  @param value to be associated with the specified key and subKey
  @return previous value associated with specified key and subKey, or null if there was no mapping for key and subKey.
  A null return can also indicate that the HashMap previously associated null with the specified key and subKey.