[英]Java 8 group map by key
I want to group a map object by key. 我想按键对地图对象进行分组。 I try with this code but i have a compile error: 我尝试使用此代码,但出现编译错误:
Non-static method cannot be referenced from a static context
My code: 我的代码:
Map<String, List<A>> getAMap() {
return Arrays.stream(SomeArray.values())
.map(map -> createObject())
.collect(Collectors.groupingBy(Map.Entry::getKey,
Collectors.mapping(Map.Entry::getValue, Collectors.toList())));
}
private Map<String, A> createObject()
final A a = new A(some attributes);
Map<String, A> map = new LinkedHashMap<>();
map.put(some key, a);
.... // add another values.
return map;
}
I need something like 我需要类似的东西
{
"a", {a1, a2, a3},
"b", {a4, a5, a6},
}
It looks like your code is wrong on some levels and that error message is not what exactly happens. 看起来您的代码在某些级别上是错误的,并且该错误消息并非确切发生的情况。
For example createObject()
returns a Map
so you get a Stream<Map<...>>
, so obviously .collect(Collectors.groupingBy(Map.Entry::getKey...
will not work. You need to change your code a bit for this to work: 例如, createObject()
返回一个Map
因此您得到Stream<Map<...>>
,因此显然.collect(Collectors.groupingBy(Map.Entry::getKey...
将不起作用。您需要更改代码一点点的工作:
Arrays.stream(someArray)
.flatMap(map -> createObject().entrySet().stream())
.collect(Collectors.groupingBy(Entry::getKey,
Collectors.mapping(Entry::getValue, Collectors.toList())));
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.