It is literally impossible to write any reasonable high performance software in Java. (Yes, I've worked with Java devs who thought they had written high performance software, but they had no point of reference). This is mostly due, among other things, to the way modern CPUs implement cache, and the way Java completely disregards this by requiring objects to be object graphs of randomly allocated blobs of memory. A language that allows for locality of access can easily be an order of magnitude faster, and with some care, two orders of magnitude.
Its "literally possible" to do this with Unsafe, and has been for a long time. You get a block of memory, the base address, then you put things in it.
Just because its not the "idiomatic java style" doesn't mean its not Java. You might do this because you can use this for the parts that really need hand-tuned performance, then rely on the JVM/ecosystem for the parts that don't need it.
