You can achieve optimized C/C++ speeds, you just can't program the same way you always have. Step 1, switch your data layout from Array of Structures to Structure of Arrays. Step 2, after initial startup switch to (near) zero object creation. It's a very different way to program Java.

You have to optimize your memory usage patterns to fit in CPU cache as much as possible which is something typical Java develops don't consider. I have a background in assembly and C.

I'd say it's slightly harder since there is a little bit of abstraction but most of the time the JIT will produce code as good as C compilers. It's also an niche that often considers any application running on a general purpose CPU to be slow. If you want industry leading speed you start building custom FPGAs.

Not necessarily. Java can be insanely performant, far more than I ever gave it credit for in the first decade of its existence. There has been a ton of optimization and you can now saturate your links even if you do fairly heavy processing. I'm still not a fan of the language but performance issues seem to be 'mostly solved'.

There are actually cases when Java (the HotSpot JVM) runs faster than the same logic written in C/C++ because the JVM is doing dynamic analysis and selective JIT compilation to machine code.

I personally know of an HFT firm that used Java approximately a decade ago. My guess would be they're still using it today given Java performance has only improved since then.

As long as you tune the JVM right it can be faster. But its a big if with the tune, and you need to write performant code

Depends. Many reasons, but one is that Java has a much richer set of 3rd party libraries to do things versus rolling your own. And often (not always) third party libraries that have been extensively optimized, real world proven, etc.

Then things like the jit, by default, doing run time profiling and adaptation.