Java 20 / JDK 20: General Availability

Post by pjmlp » Wed, Mar 22, 2023, 6:43 AM UTC

jwr wrote: post #61

As a Clojure programmer, I don't care about any of the Java language features or improvements, but I'm super happy that I'm getting a state of the art JVM that is continuously developed, maintained, extended and optimized, over a time scale of decades. This is incredibly useful: having a good VM to run your code in, with good modern garbage collectors, is not an obvious thing (as many other languages have learned). T…

Post by pjmlp » Wed, Mar 22, 2023, 6:50 AM UTC

jillesvangurp wrote: post #205

philonoist wrote: post #87

Could the pundits of HN please compare this release with Kotlin?

Picking the release notes apart: - ScopedValue (Incubator). Seems like a replacement for ThreadLocal that is intended to be a bit less dangerous (it is notorious for leaking memory and file handles). The Kotlin equivalent would be CoroutineScope. I'd say the latter is the cleaner solution. And probably ScopedValues came into existence for the same reason (co-routines & structured concurrency kind of breaking ThreadLo…

Post by kaba0 » Wed, Mar 22, 2023, 6:52 AM UTC

cesarb wrote: post #263

mike_hearn wrote: post #236

Earlier quoted context omitted.

The problem of scaling threads up further is fundamental and not really solvable by more kernel features. JVM virtual threads can be efficient because the runtime has complete knowledge of the executing code and stack layouts, how the heap is laid out, how the GC works and it can control how code is compiled. The kernel can't do any of these things - it has to assume a process is a black box that could do anything wi…

> JVM virtual threads can be efficient because the runtime has complete knowledge of the executing code and stack layouts, how the heap is laid out, how the GC works and it can control how code is compiled. Forgive me for staying doubtful, but I recall hearing this same "the JVM can be very fast and efficient because its JIT has complete knowledge and control" spiel back in the 90s, and back then, anyone could clearl…

Post by kaba0 » Wed, Mar 22, 2023, 6:55 AM UTC

tadfisher wrote: post #280

koito17 wrote: post #267

Earlier quoted context omitted.

As another Clojure programmer, I say you should care about developments in Java. After all, the Java module system is precisely why classes became minefields with clojure.core/bean -- illegal reflective accesses and what not. As someone else noted in this comment section, a lot of useful Clojure libraries are wrappers over Java libraries. So improvements to Java used in these libraries are good for you, too.

The Java module system is a problem on Java as well. They defined "module" in the narrowest terms possible (API visibility) without addressing any of the modularization problems Java developers have to deal with every day, so we end up with another layer on top of the layers of third-party dependency management systems, package repositories, and runtime class loaders that we are forced to use to have a semblance of a…

Post by kaba0 » Wed, Mar 22, 2023, 7:09 AM UTC

jgon wrote: post #252

taftster wrote: post #119

Earlier quoted context omitted.

I just wish records had an easy way to facilitate and/or associate a builder with them. Wishful thinking, out of scope for what they are. And of course, it's not hard to write a FooBuilder that's defined to help construct a Foo record. If Java records could be told to have a private constructor, I'd be completely satisfied with them. I just don't like the ability for callers to be able to directly instantiate a recor…

I wanted to experiment with creating a "Rust-like" option and result type for Java and so figured that I would need records and pattern matching for this and I ran into exactly what you are talking about here with records and public constructors. My solution was to create a sealed interface that permitted the None and Some records as the only classes to implement it. Those records are not available outside the packag…

  switch (option) {
    case Some(var x) -> println(x);
    case None -> // TODO
  }