一起迭代两个 Java-8-Streams
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Iterate two Java-8-Streams together
提问by F. B?ller
I'd like to iterate two Java-8-Streams together, so that I have in each iteration-step two arguments.
Something like that, where somefunctionproduces something like Stream<Pair<A,B>>.
我想将两个 Java-8-Streams 一起迭代，以便在每个迭代步骤中都有两个参数。类似的东西，在哪里somefunction产生类似的东西Stream<Pair<A,B>>。
Stream<A> as;
Stream<B> bs;
somefunction (as, bs)
.forEach ((a, b) -> foo (a, b));
// or something like
somefunction (as, bs)
.forEach ((Pair<A, B> abs) -> foo (abs.left (), abs.right ()));
I want to know, if Java provides something like that, although there is no Pairin Java :-(
If there is no API-Function like that, is there another way of iterating two streams simultaniously?
我想知道，如果 Java 提供了类似的东西，尽管PairJava 中没有:-( 如果没有这样的 API-Function，是否有另一种方法可以同时迭代两个流？
采纳答案by Holger
static <A, B> Stream<Pair<A, B>> zip(Stream<A> as, Stream<B> bs)
{
Iterator<A> i=as.iterator();
return bs.filter(x->i.hasNext()).map(b->new Pair<>(i.next(), b));
}
This does not offer parallel execution but neither did the original zipimplementation.
这不提供并行执行，但原始zip实现也不提供。
And as F. B?ller has pointed outit doesn't work if bsis infinite and asis not. For a solution which works for all possible combinations of infinite and finite streams, an intermediate Iteratorwhich checks both sources within the hasNextmethod seems unavoidable1:
正如F. B?ller 所指出的那样，如果bs是无限的并且as不是，则它不起作用。对于适用于无限流和有限流的所有可能组合的解决方案，Iterator在hasNext方法中检查两个源的中间体似乎是不可避免的1：
static <A, B> Stream<Pair<A,B>> zip(Stream<A> as, Stream<B> bs) {
Iterator<A> i1 = as.iterator();
Iterator<B> i2 = bs.iterator();
Iterable<Pair<A,B>> i=()->new Iterator<Pair<A,B>>() {
public boolean hasNext() {
return i1.hasNext() && i2.hasNext();
}
public Pair<A,B> next() {
return new Pair<A,B>(i1.next(), i2.next());
}
};
return StreamSupport.stream(i.spliterator(), false);
}
If you want parallel capable zipping you should consider the sourceof the Stream. E.g. you can zip two ArrayLists (or any RandomAccessList) like
如果您希望能够平行您的压缩和解应该考虑源的Stream。例如，您可以压缩两个ArrayList（或任何RandomAccessList），例如
ArrayList<Foo> l1=new ArrayList<>();
ArrayList<Bar> l2=new ArrayList<>();
IntStream.range(0, Math.min(l1.size(), l2.size()))
.mapToObj(i->new Pair(l1.get(i), l2.get(i)))
. …
1(unless you implement a Spliteratordirectly)
1（除非你Spliterator直接实现）
