是否可以在 Java 8 中转换 Stream? [英] Is it possible to cast a Stream in Java 8?
问题描述
是否可以在 Java 8 中转换流?假设我有一个对象列表，我可以做这样的事情来过滤掉所有额外的对象:
Is it possible to cast a stream in Java 8? Say I have a list of objects, I can do something like this to filter out all the additional objects:
Stream.of(objects).filter(c -> c instanceof Client)
在此之后，如果我想对客户做某事，我需要对每个客户进行强制转换:
After this though, if I want to do something with the clients I would need to cast each of them:
Stream.of(objects).filter(c -> c instanceof Client)
.map(c -> ((Client) c).getID()).forEach(System.out::println);
这看起来有点难看.是否可以将整个流转换为不同的类型?就像将 Stream 强制转换为 Stream?
This looks a little ugly. Is it possible to cast an entire stream to a different type? Like cast Stream<Object> to a Stream<Client>?
请忽略这样一个事实，做这样的事情可能意味着糟糕的设计.我们在我的计算机科学课上做这样的事情，所以我正在研究 Java 8 的新特性，并很好奇这是否可能.
Please ignore the fact that doing things like this would probably mean bad design. We do stuff like this in my computer science class, so I was looking into the new features of java 8 and was curious if this was possible.
推荐答案
我认为没有一种开箱即用的方法.一个可能更清洁的解决方案是:
I don't think there is a way to do that out-of-the-box. A possibly cleaner solution would be:
Stream.of(objects)
.filter(c -> c instanceof Client)
.map(c -> (Client) c)
.map(Client::getID)
.forEach(System.out::println);
或者，如评论中所建议的，您可以使用 cast 方法 - 不过前者可能更容易阅读:
or, as suggested in the comments, you could use the cast method - the former may be easier to read though:
Stream.of(objects)
.filter(Client.class::isInstance)
.map(Client.class::cast)
.map(Client::getID)
.forEach(System.out::println);
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