In addition, Apple's Accelerate framework makes it easy and natural to take advantage of SIMD for further speedups — you can get powerful vector operations with single function calls. This seems to have no Android equivalent.
Renderscript?
s/idiomatic/pure/
However, implying that "require a hash table lookup" is slow isn't really right. The message send implementation is extremely optimized and takes about a dozen CPU cycles to execute last I measured. To put that in perspective, that means that an Objective-C message send on the fast path (which happens 99.99% of the time, the slow path basically just happens once per message/class combo) costs about as much as two C function calls, or one and a half C++ virtual function calls.
Message send overhead in a typical Objective-C app is small. 10% would be high, for really message-heavy code, and 5% is more typical. Most Objective-C code is not messaging so it's still fast.
Take these benchmarks as an example. To write them in "idiomatic Objective-C" you'd change almost nothing. You'd either get rid of the few C++-isms (templates for min/max functions, parameters passed by reference, no big deal) or compile the file as Objective-C++. You'd never write code like this using Objective-C objects. In addition to be slower, it would be harder to write, harder to read, and much larger.
My point was really that Objective-C isn't always faster than the equivalent Java (a function call, hash lookup and jump is fast in most contexts, but it's still infinitely slower than nothing, which is the overhead of a JIT-inlined method call), but that being a superset of either C or C++ means that it can be faster when it needs to be. Which is ultimately what matters.
However, my point is that not only can you write faster Objective-C code, but that most normal Objective-C code will be faster, because most normal Objective-C code isn't that message heavy. So it's not just that it can be faster, but that it usually will be. Typically. Depending on what you're doing.
Kinda. I imagine that if these benchmarks were run on idiomatic Objective-C, they'd be an order of magnitude slower than Java. All method calls are un-inlineable and often require a hash table lookup to resolve.
However, the nice thing about Objective-C is that it's ridiculously easy to write performance-critical stuff in C or C++, then expose it with a nice OO interface. Which means that you (or, more likely, the people who wrote the library you're using) are more likely to bother. That and the lack of GC making latency easier to reason about.
So while it is probably easier to write performant UIs in Objective-C than Java, it isn't because of the reasons mentioned here.