![](/img/trans.png)
[英]How does Java decide to sort a list of objects with multiple fields, when the chosen field to compare the object is equal?
[英]Sort list by multiple fields(not then compare) in java
现在我有一个 object:
public class Room{
private long roomId;
private long roomGroupId;
private String roomName;
... getter
... setter
}
我想按“roomId”对房间列表进行排序,但与此同时,房间对象的“roomGroupId”大于零并且具有相同的值,然后使它们彼此靠近。 让我举个例子:
输入:
[{"roomId":3,"roomGroupId":0},
{"roomId":6,"roomGroupId":0},
{"roomId":1,"roomGroupId":1},
{"roomId":2,"roomGroupId":0},
{"roomId":4,"roomGroupId":1}]
output:
[{"roomId":6,"roomGroupId":0},
{"roomId":4,"roomGroupId":1},
{"roomId":1,"roomGroupId":1},
{"roomId":3,"roomGroupId":0},
{"roomId":2,"roomGroupId":0}]
如上所示,列表按 'roomId' 排序,但 'roomId 4' 和 'roomId 1' 靠得很近,因为它们具有相同的 roomGroupId。
这没有简单的好解决方案(也许我错了)。
你可以这样做
TreeMap<Long, List<Room>> roomMap = new TreeMap<>();
rooms.stream()
.collect(Collectors.groupingBy(Room::getRoomGroupId))
.forEach((key, value) -> {
if (key.equals(0L)) {
value.forEach(room -> roomMap.put(room.getRoomId(), Arrays.asList(room)));
} else {
roomMap.put(
Collections.max(value, Comparator.comparing(Room::getRoomId))
.getRoomId(),
value
.stream()
.sorted(Comparator.comparing(Room::getRoomId)
.reversed())
.collect(Collectors.toList())
);
}
});
List<Room> result = roomMap.descendingMap()
.entrySet()
.stream()
.flatMap(entry -> entry.getValue()
.stream())
.collect(Collectors.toList());
如果你在 Java 8,你可以使用这样的代码
Collections.sort(roomList, Comparator.comparing(Room::getRoomGroupId)
.thenComparing(Room::getRoomId));
如果没有,您应该使用比较器
class SortRoom implements Comparator<Room>
{
public int compare(Room a, Room b)
{
if (a.getRoomGroupId().compareTo(b.getRoomGroupId()) == 0) {
return a.getRoomId().compareTo(b.getRoomId());
}
return a.getRoomGroupId().compareTo(b.getRoomGroupId();
}
}
然后像这样使用它
Collections.sort(roomList, new SortRoom());
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.