Hanging on the telephone

Inside RoboVM


Some said it couldn’t be done. Others said it shouldn’t. But this developer is actively scaling out a future for Java in the iOS. Here‘s his story.

Bringing Java to the iOS is somewhat of a mobile holy grail. But
there‘s one developer who wants to give it his all. In this
interview, Peter Friese speaks to Niklas Therning, the man behind
the RoboVM open-source project and co-founder of Trillian Mobile AB
– the main contributor to the RoboVM project – which is aiming to
make the Java iOS leap come true.

JAX: Can you tell us a little about

Niklas Therning: My name is
Niklas Therning. I’m 36 years old and I live in Gothenburg, Sweden.
I’ve always had an interest in computers and I have been
programming since the early 90s when I got my Amiga 500. I have an
MSc in computer engineering from Chalmers, Gothenburg. For the past
10 years I have been working in my own company doing contract work,
mainly server side Java and web app development. I also co-founded
the SpamDrain anti-spam service (http://spamdrain.net) where I have
been doing not only frontend and backend coding but also customer
support and server administration. For the past 3 years or so I
have been working on RoboVM, first as a side-project in my spare
time and then full-time for the past 1.5 years roughly.

Who is working on RoboVM?

Mostly me only. There’s a small community around
the project but except for testing (which is awesome!) it doesn’t
contribute very much yet. I think this is normal for any young
open-source project. It takes time to build a community that is
more involved. I must admit that I could probably do more to
facilitate for contributors, e.g. by writing proper documentation
of the RoboVM internals.

How is it funded?

So far RoboVM has been funded by our company,
SpamDrain AB. But since a few weeks back we’ve managed to secure
some seed-funding. This should give us a needed boost and we will
soon hire some more developers to work on the project.

How did you come up with the idea for

Back in 2010 we started to build iOS and Android
apps for SpamDrain. We did look into the different cross-platform
tools that were available at that time. We didn’t want to build an
HTML5/JS/CSS app so that ruled out almost all of the tools. And
since all of us had extensive Java knowledge and this being the
native language on Android we would have preferred something based
on Java. We didn’t find anything to our liking so we went with
Xcode and Objective-C for the iOS app in the end. This made me
start to think about how one could get Java running under iOS.
Xamarin had already shown that it could be done for C# with
MonoTouch so why shouldn’t it be possible for Java?

How does it relate to Xamarin?

RoboVM is very similar to Xamarin in the way it
works except that they let you use C# and .NET technologies while
RoboVM lets you use Java and other JVM languages and Java platform
technologies and tools.

And how about XMLVM?

At a high level it’s quite similar to XMLVM in
the way it takes Java bytecode and transforms it into machine code.
Their process looks like bytecode->XML->C->machine code
while ours is bytecode->Soot Jimple->LLVM IR->machine
code. I haven’t really looked at it closer than that.

In comparison to Objective-C, Java is a much
more verbose language Where do you see the sweet spots for

Before I answer this one I would like to know
how you think Java is “much more verbose”? I don’t agree with that
statement. Please prove me wrong. :-)

RoboVM is not limited to Java. In theory you
could use any language that targets the JVM. Scala, Kotlin and
Clojure are other JVM languages that are known to work with RoboVM
and those fixes many of the shortcomings of the Java

The main use case for RoboVM as I see it is the
possibilities to share code between Android and iOS apps and for
Java developers to reuse their skills, not having to learn a new
language and new tools.

Objective-C has a very distinctive method
naming pattern that does not translate well to most other
languages. How do you translate method names from Objective-C to
Java? Do you write the mappings manually, or do you use an
automated approach?

I use a semi-automated process. I have a tool
that reads ObjC header files and a config file and spits out Java
class files. The config file can contain things such as method
rename rules and info on where a global function should end up
(there’s no global scope in Java). Method names are changed
slightly to look more natural to Java programmers and shortened
(usually by cutting before the first : in the selector

Most apps that have been published on the app
store seem to be games. Is this a sweet spot for

Not really. When I started working on RoboVM I
thought that games would be the least likely type of apps to use it
due mainly to the garbage collection and potential “stop the world”
pauses. But then the libgdx community showed a great interest in
the project and I started to help them out to get a working
RoboVM/iOS backend. Using libgdx one can now use a single code base
to write games for Android, Blackberry, desktop, HTML5 and iOS.
Even with 50+ libgdx based games already in the App Store I have
heard very few comments about the GC being a problem. The libgdx
community has been awesome by testing the code at a very early
stage. I’m very grateful for their help.

What are your plans for IDE integrations and
other developer tooling? Currently, you have an Eclipse
integration, but people have been asking for IntelliJ

IntelliJ integration is the most commented issue
on our Github page. At some point we will have to look into it if
no one in the community jumps in. We already provide Maven
integration and people in the community have done Gradle, sbt and
Leiningen plugins. The JavaFX community and Oracle have done
Eclipse and Netbeans JavaFX plugins that facilitate building JavaFX
apps for iOS.

In the future we will have to provide a debugger
and JUnit integration. It would also be nice to have some kind of
Interface Builder integration.

What is the roadmap for RoboVM?

The goal is the have a stable version (1.0)
sometime late Q3 or early Q4. Apart from being reasonably bug free
this should include completed and tested CocoaTouch bindings and
have proper documentation. We will start to offer some kind of
commercial licenses around the project similar to what Xamarin does
with the big difference that RoboVM has a fully useable open-source
core which you can use to develop apps without any

Niklas Therning is the founder of the RoboVM
open-source project and co-founder of Trillian Mobile AB – the main
contributor to the RoboVM project. He has made it his mission to
bring Java to iOS and do it properly. Before starting RoboVM Niklas
co-founded the SpamDrain anti-spam service and worked as a
contractor, mostly doing Java EE and web app development. Niklas
holds a Master of Science degree in Computer Engineering from
Chalmers University of Technology, Gothenburg, Sweden.

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