Why is Stream<T> not an Iterable<T> ?

Oliver Doepner odoepner at gmail.com
Tue Mar 26 19:56:10 PDT 2013


I recently joined this mailing list. I am quite excited about the
lambda functionality coming in Java 8.
I also had the pleasure to attend Brian's "Road to Lambda" talk at JavaOne.
Thanks for the great work.

Today I looked at the Javadoc at

I hope that site has recent information. I had some problems finding
the source itself on hg.
I probably misunderstood the (not so obvious?) links at

Anyhow, I noticed that both of the methods of Iterable (iterator,
forEach) are also present on Stream.
Now I wonder why Stream<T> does not extend Iterable<T>.

Then I searched the lambda-dev archives for threads related to Iterables.
I did not find a discussion directly related to this. I hope I didn't
miss anything.

I think that it would be nice if Stream instances could be passed to
existing APIs that take Iterable.

Naively speaking: Why have the same methods with the same signatures
and semantics / Javadoc on two core Java interfaces and not make one a
subtype of the other? That feels like a pair of quack-like-a-ducks
calling for subtyping. :^)


Oliver Doepner

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