Java 8 lambda : Comparator

Question

我想用 Lambda 对列表进行排序:

List<Message> messagesByDeviceType = new ArrayList<Message>();      
messagesByDeviceType.sort((Message o1, Message o2)->o1.getTime()-o2.getTime());

但是我得到了这个编译错误:

 Multiple markers at this line
    - Type mismatch: cannot convert from long to int
    - The method sort(Comparator<? super Message>) in the type List<Message> is not applicable for the arguments ((Message o1, Message o2) 
     -> {})

Answer 1

Comparator#compareTo 返回一个 int；而 getTime 显然是 long.

这样写会更好:

.sort(Comparator.comparingLong(Message::getTime))