Taking Java further

Eclipse Xtend: Java’s equivalent to CoffeeScript


We speak to Sven Efftinge and Sebastian Zarnekow about their new JVM-based programming language that compiles into readable Java code.

the June edition of JAX
, Sven Efftinge and Sebastian Zarnekow introduce us to
their new JVM-based programming language that compiles into
readable Java code, Xtend.

JAX: Can you give us a brief description of

Sebastian Zarnekow: Xtend is a statically typed
programming language running on the Java Virtual Machine. It’s
designed to jazz up Java a little, to address the weaknesses that
Java has accumulated over the years. Our goal is not to abandon
Java altogether, but rather to complement it, so that it can be
integrated into in any given project. The idea is to make it
possible to draw on Xtend in any Java project situation, so that
one can find smoother solutions to one’s problems.

JAX: You were just talking about Java’s
weaknesses. Can you elaborate on what weaknesses Xtend

Sven Efftinge: Principally, Java is a relatively
well-designed language. The upside is that there are little
surprises compared to other languages. The downside is that it’s
quite old and what they call ‘ceremonious’, meaning you have to
communicate with the compiler a lot, you need to write down a lot
of types twice, and use brackets and semicolons everywhere; you
don’t have closures or lambda expressions; if you want to use
JavaBeans you have to call Getters and Setters; there is no
operator overloading. All those problems were solved in Xtend, in a
way that is very easy to understand. And since Xtends immediately
compiles to Java code, you can always see what you are doing. It’s
perfectly readable, it’s like CoffeeScript for JavaScript.

JAX: There are other languages that pursue
similar goals, though. What sets Xtend apart from, say,

Efftinge: Groovy has a similar thrust, but is a
few years older. We adopted many good ideas from Groovy, but also
from Scala and from Java. Unlike Groovy, Xtend is statically typed,
with the same type system as Java, including generics, which are
exactly the same, just as the conversion rules. What this means is
that the ten million developers out there who know Java will
understand it immediately. In addition, there is much better
tooling: you get content assist and compiler checks in Eclipse, all
the things you’re used to from Java. The code that is generated is
very fast compared to Groovy. A well-known problem with Groovy is
that it’s fairly slow.

Compared to Scala – it’s simpler! That’s the most important
difference. You can use different IDEs for the language because the
type system is not as extreme.

JAX: The two of you are also the key men
behind Xtext. What’s the connection between Xtend and

Zarnekow: That’s quite an interesting question.
Basically, what we did with Xtend was to create a full-blown
programming language based on Xtext, in the course of which we
developed a reusable expression language for Xtext that is now
embeddable into any domain-specific language. It’s now possible to
build nice APIs with Xtend and one can generate very readable code
by means of concepts such as extension functions, operator
overloading etc. In certain situations one might still get to the
point where the abstractions are not sufficient, but since Xtend is
based on Xtext, it allows for exceptionally good integration with
external DSLs, so that one can operate seamlessly between Xtend and
Java or Xtend and a DSL within one and the same project. This is
another one of Xtend’s unique features.

JAX: Any specific projects you have tackled so
far, using Xtend? If so, which ones?

Efftinge: Xtend is still very, very young. We
released a preview version as part of Eclipse’s release train last
summer (Indigo, editor’s note), followed by a minor release last
winter. A really interesting release is coming up in June, as part
of the next release train (Juno, editor’s note). It will be very
well integrated, and the language will be quite complete

We make extensive use of Xtend in our own projects. Many people
start using it for JUnit testing, because there it’s interesting to
have a good syntax and compact test cases so that you are actually
able to see the test data. With Xtend, you can generate great
builder syntax and multi-line strings. So that’s where it’s used a
lot. The Google Group have used Xtend for Android development and
GWT. The great advantage is that it translates to Java code rather
than bytecode, so you can use any platform that works with Java
source code, such as GWT, which translates to JavaScript. This is
not quite as easy with Scala.

So, in general, no big projects so far, but a lot of people have
just started experimenting with it, they find it exciting – and I’m
curious to see first results. We’re mainly involved in open-source
development. We support customers developing languages with Xtext,
and when it comes to building things like code generators, Xtend
comes in handy. But so far, we haven’t written any big business
applications using Xtend.

JAX: The final question’s for you, Sven: You
won one of this year’s Eclipse Community Awards. You were honored
as Top Committer. What does this award mean to you?

Efftinge: It made me very happy, obviously –
especially because the award winners are selected by the community.
It’s not like the decision is made by a jury of five people, but
the entire community is allowed to vote. It’s a great award.
Sebastian won it last year, by the way, so let’s wait and see who’s

This interview was originally conducted in German by
Hartmut Schlosser and Diana Kupfer at JAX in Mainz, on April 19,
2012. It has also been published in our sister publication,



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