在 Java 8 中用流替换嵌套 for 循环的正确方法是什么？
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What is the proper way of replacing a nested for loop with streams in Java 8?
提问by Pierre Henry
While learning Java 8 streams and lambas, I tried to replace the following nested for loops with streams :
在学习 Java 8 流和 labas 时，我尝试用流替换以下嵌套的 for 循环：
List<Long> deskIds = new ArrayList<>();
for(ProvidedService memberService : service.getAllNodesDepthFirst()){
for(Desk d : memberService.getDesks()){
deskIds.add(d.getId());
}
}
The loop iterates a list of 'ProvidedService' objects, and for each one, iterates over a list property of 'Desk' objects, and extracts the 'Id' field to a list.
该循环迭代“ProvidedService”对象的列表，对于每个对象，迭代“Desk”对象的列表属性，并将“Id”字段提取到列表中。
I came up with the following code using streams :
我想出了以下使用流的代码：
List<Long> deskIds = new ArrayList<>();
service.getAllNodesDepthFirst().stream().forEach(srv -> {
deskIds.addAll(srv.getDesks().stream().map(Desk::getId).collect(Collectors.toList()));
});
Is it the proper/optimal way to do it ? Or is there a way to do this without the second nested stream ?
这是正确/最佳的方法吗？或者有没有办法在没有第二个嵌套流的情况下做到这一点？
回答by assylias
I would probably write it like this:
我大概会这样写：
List<Long> deskIds = service.getAllNodesDepthFirst().stream()
.flatMap(p -> p.getDesks().stream())
.map(Desk::getId)
.collect(toList());
