[英]Java 8 stream for-loop
Im new to Java 8 Streams and would like to convert following code-block to Java 8's Stream way of doing the same thing. 我是Java 8 Streams的新手,并希望将以下代码块转换为Java 8的Stream方式来做同样的事情。
Edit : Updates the class-names to be less confusing. 编辑 :更新类名称以减少混淆。 (Removed Foo, Bar, Baz...)
(删除了Foo,Bar,Baz ...)
ArrayList<PriceList> priceLists = new ArrayList<PriceList>();
// I'm casting to a type-safe List from getObjects()
// -which is a function I dont have access to. Is there a nice
// solution to embed this in the stream-syntax?
List<PriceListGroup> distObjects = (List<PriceListGroup>) objects.get(1).getObjects();
for(PriceListGroup group : distObjects) {
Set<Affiliate> affiliates = group.getAffiliates();
for(Affiliate affiliate : affiliates) {
priceLists.add(affiliate.getPriceList());
}
}
All help & explanation appreciated 所有帮助和解释表示赞赏
You can do it with flatMap
: 你可以用
flatMap
做到这一点:
List<FooBO> list1 = objects.get(1).getObjects().stream()
.flatMap (b -> b.getAffiliates().stream())
.map(BazBo::getPriceList)
.collect(Collectors.toList());
Edit : 编辑:
Since objects.get(1).getObjects()
seems to return a List<Object>
, a cast is required. 由于
objects.get(1).getObjects()
似乎返回List<Object>
,因此需要objects.get(1).getObjects()
。 To be safe, you can also add a filter that makes sure the type of the Object
s is indeed BarBO
prior to the cast : 为了安全起见,您还可以添加一个过滤器,以确保在
BarBO
之前Object
的类型确实是BarBO
:
List<FooBO> list1 = objects.get(1).getObjects().stream()
.filter (o -> (o instanceof BarBo))
.map (o -> (BarBO)o)
.flatMap (b -> b.getAffiliates().stream())
.map(BazBo::getPriceList)
.collect(Collectors.toList());
EDIT : 编辑:
Here's an answer with the class names of the edited question: 以下是已编辑问题的类名的答案:
List<PriceList> priceLists =
distObjects.stream()
.flatMap (g -> g.getAffiliates().stream())
.map(Affiliate::getPriceList)
.collect(Collectors.toList());
Considering your classes (in the example that you provided and assuming it compiles at least), I don't really understand why flatMap two times would not work: 考虑你的类(在你提供的示例中并假设它至少编译),我真的不明白为什么flatMap两次不起作用:
List<BarBO> input = new ArrayList<>();
List<FooBO> result = input.stream()
.flatMap((BarBO token) -> {
return token.getAffiliats().stream();
})
.flatMap((BazBO token) -> {
return token.getPriceList().stream();
})
.collect(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.