[iheartmemcache]

When I think of API I think of "here is your interface eBNF"

    (interface)* = (class)* 
    (class) = (method_stub)* | (ivar)* | (class_var)*  |(property}* | {delegate}* | {some_LINQy_constructs}* | {other_stuff_from_NETCLR3.5_onwards}* | ... 
    . 

"Alright, now implement IEnumerator OnNext(); bool MoveNext(); IDisposible Dispose();"[1] and your data now has the trait/type-class/whatever of IEnumerable! That's all an API is really -- method signatures and code contracts between the requester/requestee. The real gold isn't in that, but in the implementation details of the JVM (and the greybeards who know the -Xxs256 -Xmm10230 blah blah, I suppose.)

I.e. Azul ZING(tm) and the lot of insanely high-performance and/or hard-real-time-in-the-QNX-sense is priced at... a lot. In finance we used to use it because operations could be bounded deterministically. There was enough value in that that CTOs cut 7 figure checks to run that specific API implementation rather than use the Sun/Oracle JVM.

[1] Yep that's probably gobblydygook. My C# and Java meld together, I always confuse IEnumerable,IEnumerator,IDispose,and all the damn duals smash together in my mind, even worse now with Rx one more tensor rank was added (Time). Gods of the CoreCLR, smite me not. Also I'm not in PL design, forgive my bad BNF.