Collections 最大值，最小值

 for(RoomBillSysRoomCrmGuest roomBillSysRoomCrmGuest : roomBillSysRoomCrmGuests){
                 Date inDate = roomBillSysRoomCrmGuest.getCheckInTime();
                 checkInTimes.add(inDate.getTime());
                 Date outDate = roomBillSysRoomCrmGuest.getCheckOutTime();
                 checkOutTimes.add(outDate.getTime());
             }
             Long minNumber =  Collections.min(checkInTimes);
             Long manNumber =  Collections.max(checkOutTimes);