在java中连接来自同一对象的2个流

Question

I have a list of objects of class A defined as below:

class A {
    private Set<String> sOne;
    private Set<String> sTwo;
    // Constructor, getters and setters
}

Now I would like to create a stream which contains elements of both sOne and stwo . Is there a way to do it in Java 8?

Answer 1

Stream.concat(sOne.stream(), sTwo.stream())

您应该知道，在某些情况下，这会降低某些特征IIRC。

Answer 2

You can combine them using:

List<A> aList = ...;

Stream<String> stream = aList.stream()
                             .flatMap(a -> Stream.concat(
                                      a.getsOne().stream(), 
                                      a.getsTwo().stream())
                              );

Answer 3

An alternative to already mentioned Stream::concat is the Stream::of :

Stream.of(sOne.stream(), sTwo.stream())
      .flatMap(Function.identity())
      ...

This requires to flatten the structure unless you wish to work with Stream<Stream<T>> or a stream of any collection Stream<Collection<T>> .