问题描述
使用 Java 8 lambda 表达式，我正在尝试做这样的事情.
Using a Java 8 lambda expression, I'm trying to do something like this.
List<NewObject> objs = ...;
for (OldObject oldObj : oldObjects) {
NewObject obj = oldObj.toNewObject();
obj.setOrange(true);
objs.add(obj);
}
我写了这段代码.
oldObjects.stream()
.map(old -> old.toNewObject())
.forEach({new.setOrange("true")})
.collect(Collectors.toList());
这是无效代码，因为我试图对 .forEach() 返回的内容执行 .collect()，但 forEach 无效且不返回列表.
This is invalid code because I'm then trying to do .collect() on what's returned by .forEach(), but forEach is void and does not return a list.
这应该如何构建?
推荐答案
你可以使用Stream的peek方法，返回Stream 因为它是一个中间操作.它通常不应该有副作用(它应该是无干扰的")，但在这种情况下，我认为副作用 (setOrange(true)) 是有意的并且是很好.
You can use Stream's peek method, which returns the Stream because it's an intermediate operation. It normally isn't supposed to have a side effect (it's supposed to be "non-interfering"), but in this case, I think the side effect (setOrange(true)) is intended and is fine.
List<NewObject> newObjects =
oldObjects.stream()
.map(OldObject::toNewObject)
.peek( n -> n.setOrange(true))
.collect(Collectors.toList());
它与您的非流代码一样冗长，因此您可以选择使用哪种技术.
It's about as verbose as your non-streams code, so you can choose which technique to use.
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