hourly_totals 是一个对象从一个小时表示为一个字符串到另一个对象，到Map ，其中 T 是表示一小时数据的 POJO 类，看起来是一个自然的选择.

hourly_totals is an object from an hour represented as a string to another object, to Map<String,T> , where T is a POJO class representing the data for one hour, would look like a natural choice.