Are you saying that the Java benchmarks linked above are written using "magic hacks"? None of them are even close to a 10x gap, despite the fact that some of the C++ ones do use magic hacks (vector intrinsics).
10x gaps occur whenever you have to interface Java with the real world—disks, memory, CPUs, virtual memory subsystems, networking stacks, etc. to get high-performance.
That's why Cassandra has so much C++ in it, and why ScyllaDB is so much faster still.
It's not the C++ per se is "faster" than Java, it's what C++ lets you easily do that Java doesn't.
Other comments have said—well, Java is more maintainable. That's also highly-dependent on the context. ScyllaDB has a much better developer velocity than Cassandra, too. (Anyone can easily verify this.) I use the Cassandra/ScyllaDB example frequently because they implement the same spec, and do so in a compatible way.
It's also really easy to put C++ on the fast path, by adding Python to the mix. For "business logic"-like situations (supposedly the bread and butter of Java), that's what actual companies do, here on Earth, with people: use Python for the easy stuff.
I like Java, and there are certainly some very high-performance Java projects (LMAX, Aeron) and it's very productive, has great tooling, and tons of libraries. There's nothing wrong with it. You can even layer more productive languages on top of the JVM. Win.
What I have a problem with are claims that "all this C++ code can be replaced with Java" at some hand-wavey minor cost. That's…not true.
People are not stupid, they use C++ today because it can do the job when nothing else really can—Java included.
P.s. It's not even true that Java allows you to "forget about memory management". I don't know why people keep saying that, but it's objectively false. If you care about performance, you have to be aware of memory allocations. The GC is not some magic "make my code run fast" card.
Furthermore, there are so many kinds of resources beyond memory! And the GC is an impediment in many cases to using those kinds of resources effectively. C++ has an extremely good story when it comes to managing every kind of computing resource in a large, maintainable codebase.
> 10x gaps occur whenever you have to interface Java with the real world—disks, memory, CPUs, virtual memory subsystems, networking stacks, etc. to get high-performance.
As noted before, the CPU- and memory-intensive benchmarks upthread don't even show a factor of 10x. Despite the fact that the C++ is heavily hand-optimized in ways that are not accessible to Java programs, and the benchmarks being very short running, so heavily penalizing Java's JIT compilation. Please come off the 10x horse, it makes you look like you are arguing from prejudice, not from data. Even for hyperbole 10x is way too much.
I have experience working on high-performance compilers for both Java and C++, and I can promise you that Java compilers don't generate so very different code for using the CPU or memory. Yes, Java has some overheads, but it also has some tricks up its sleave.
