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Introducing Erjang: Erlang for the JVM

JAX Editorial Team

Where have you been all this time? Erjang takes the nifty language of Erlang to the JVM.

You’ve probably heard of Erlang, the programming
language and runtime system. But have you ever come across its Java

Any developer that appreciates a good old word play
(most) will remember the name: Erjang, the runtime tool that takes
Erlang programs and runs them on the Java Virtual Machine.

With built-in support for concurrency, distribution and fault
tolerance, Erlang has established itself as an effective language
for scalable real-time systems in industries like e-commerce,
banking and instant messages. Seems logical to introduce it to the
wonderful world of Java, right?

Erlang for the JVM

This is how it works: Erjang loads Erlang’s binary
.beam files and converts them into the Java .class file format. The
Java classes are then transferred to the JVM and executed. There’s
also a BEAM interpreter, which is still rather slow, but at the
same time, it uses less memory than the official equivalent.

But wait, does this really work? If you ask the Erjang
virtual machine’s official website “Yes! It does actually work.
Though there are exceptions…”

There’s a couple of restrictions that Java developers
need to stomach when working with Erjang. For example, runtime
support is missing from several of the BEAM instructions. On top of
that, some of the built-in Erlang functions (BIFs) are not yet, or
only partially, available. Nevertheless, the goal is to continue
expanding Erjang to allow for Java implementations of all BIFs.

Why the need for Erjang?

Erjang was unveiled in 2009 by its creator Kresten
Krab Thurup, and since then it’s been continuously developed. Even
back then, Java developers were
why even bother porting Erlang for the JVM. Isn’t
BEAM already a good enough virtual machine for Erlang?

Kresten said the main reasons were the quality of the
JVM, the potential for better performance, the enhancement of
Erlang with an alternative implementation and the besser
availability of the language for the Java community. Beyond that,
the desire to experiment and mess around with modifications proved
enough of a motivation for Kresten:

Why are you doing this? Good question. Well, I just
wanted to learn Erlang, and it seems to be working!

Erjang is available for free at http://erjang.org/. The most recent
version is 0.2, which is designed for Java 7. If this introduction
has whet your appetite, check out the video below for a nice
introduction from the creator of Erjang, Kresten Krab Thorup
himself. You can also take a look at the readme on
 and the following video

Feature image:
Satisfied customer
via Shutterstock / copyright: Everett

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