我有课-
public class LocationStats {
private String state;
private String country;
private int latestTotalCases;
private int diffFromPrevDay;
private int diffFromPrev2Day;
private int diffFromPrev3Day;
}
我在摘要下方使用的某个国家/地区的总总结数最高,效果很好。
List<LocationStats> newStats= getData();
Map<String, Integer> collect =
newStats
.stream()
.collect(Collectors.groupingBy(LocationStats::getCountry, Collectors.summingInt(LocationStats::getLatestTotalCases)));
我还想在处理上述代码段时总结其他3个属性。可能吗 ?有什么Lambda-elegant方法可以实现吗?
您可以将Collectors.toMap
与合并功能一起使用。
例如:
Map<String,LocationStats> sums =
newStats.stream()
.collect(Collectors.toMap(LocationStats::getCountry,
Function.identity(),
(s1,s2)->new LocationStats(s1,s2)));
[您必须创建一个接受两个LocationStats
实例的LocationStats
构造函数,并创建一个包含这两个实例的属性之和的实例:
public LocationStats (LocationStats s1, LocationStats s2)
{
this.state = s1.state;
this.country = s1.country;
this.latestTotalCases = s1.latestTotalCases + s2.latestTotalCases;
this.diffFromPrevDay = s1.diffFromPrevDay + s2.diffFromPrevDay;
this.diffFromPrev2Day = s1.diffFromPrev2Day + s2.diffFromPrev2Day;
this.diffFromPrev3Day = s1.diffFromPrev3Day + s2.diffFromPrev3Day;
}