[英]Collecting lists from an object list using Java 8 Stream API
I have a class like this我有这样的课
public class Example {
private List<Integer> ids;
public getIds() {
return this.ids;
}
}
If I have a list of objects of this class like this如果我有一个像这样的此类的对象列表
List<Example> examples;
How would I be able to map the id lists of all examples into one list?我如何能够将所有示例的 id 列表映射到一个列表中? I tried like this:我试过这样:
List<Integer> concat = examples.stream().map(Example::getIds).collect(Collectors.toList());
but getting an error with Collectors.toList()
但是Collectors.toList()
出现错误
What would be the correct way to achive this with Java 8 stream api?使用 Java 8 流 api 实现这一目标的正确方法是什么?
Use flatMap
:使用flatMap
:
List<Integer> concat = examples.stream()
.flatMap(e -> e.getIds().stream())
.collect(Collectors.toList());
Another solution by using method reference expression instead of lambda expression:使用方法引用表达式而不是 lambda 表达式的另一种解决方案:
List<Integer> concat = examples.stream()
.map(Example::getIds)
.flatMap(List::stream)
.collect(Collectors.toList());
您可以使用 flatMap 替代 stream.map
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.