[英]Sort list by multiple fields(not then compare) in java
Now I have an object:现在我有一个 object:
public class Room{
private long roomId;
private long roomGroupId;
private String roomName;
... getter
... setter
}
I want sort list of rooms by 'roomId', but in the meantime while room objects has 'roomGroupId' greator than zero and has same value then make them close to each other.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。 Let me give you some example:
让我举个例子:
input:输入:
[{"roomId":3,"roomGroupId":0},
{"roomId":6,"roomGroupId":0},
{"roomId":1,"roomGroupId":1},
{"roomId":2,"roomGroupId":0},
{"roomId":4,"roomGroupId":1}]
output: output:
[{"roomId":6,"roomGroupId":0},
{"roomId":4,"roomGroupId":1},
{"roomId":1,"roomGroupId":1},
{"roomId":3,"roomGroupId":0},
{"roomId":2,"roomGroupId":0}]
As shown above, the list sort by 'roomId', but 'roomId 4' and 'roomId 1' are close together, because they has the same roomGroupId.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。
This does not have easy nice solution (maybe I am wrong).这没有简单的好解决方案(也许我错了)。
You can do this like this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());
If you're in Java 8, you can use code like this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));
If not, you should use a comparator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();
}
}
and then use it like this然后像这样使用它
Collections.sort(roomList, new SortRoom());
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