It’s rare these to read stories of software billionaires and think it’s well deserved. This is one of those rare cases. Also, IntelliJ runs on Java, for all the bashing that Java gets on HN, it’s an example of how “what technology you pick is less important than your focus on user experience”. It’s amazing that their products are so performant on Java
The main issues people assume with Java are that it has slow runtime and it's verbose.
But the JVM is actually rather fast. Especially compared to JavaScript and Python, which aren't even compiled (and which I still agree with the "it's crap" hivemind). Anything that needs real performance you should be outsourcing to C/C++ FFI calls, and as long as you do that your Java app's performance should be OK. And a key cause of Java's big slowdown are checks e.g. for null-pointers and casts, which are much better than C++/Rust's approach of being unsafe-by-default.
Java is verbose, but JetBrain's awesome IDE single-handedly fixes this problem - writing POJOs and using long-named functions and classes is fast, and IntelliJ will hide excess boilerplate so that even reading code is easier. And if verbosity is still too much of an issue, there are JVM alternatives like Kotlin.