Lost in translation

Google tool J2ObjC translates Java to Objective-C

Elliot Bentley

Android manufacturer releases open-source tool for translating Java code to Apple-friendly Objective-C.

hell frozen over? Last night, Google
an open-source command-line tool for translating
chunks of Java code to Objective-C, in effect making it easier to
port Android apps to iOS.

Currently “between alpha and beta quality,” J2ObjC enables Java code to
be part of an iOS application’s build, without any additional
editing of the generated files – well, in theory. It’s apparently
already in use in several Google apps, though they warn that each
new app tends to bring to light “new bugs to be fixed”.

While primarily a tool designed to help port Android apps to iOS
platforms like the iPhone and iPad, there’s no reason J2ObjC
couldn’t be used to translate Java written for non-Android apps to
Apple platforms.

Objective-C is, of course, the language of choice for Mac OS X apps
as well as iOS apps – though this is probably less interesting,
considering that Java apps run pretty well on OS X without any
extra tinkering.

It’s worth noting this is no magical translator for porting Android
apps directly to iOS. The project’s Wiki page emphasises that
J2ObjC “does not provide any sort of platform-independent UI
toolkit,” and that “iOS UI code needs to be written in Objective-C
or Objective-C++ using Apple’s iOS SDK,” meaning a basic level of
Objective-C knowledge is still required.

J2ObjC “supports most Java language and runtime features required
by client-side application developers, including exceptions, inner
and anonymous classes, generic types, threads and reflection”, but
the most interesting technical detail is how it handles memory
management: after all, Objective-C lacks Java’s handy garbage

The tool utilises one of three native OS X methods of memory
management: reference counting, garbage collection, or the newer
Automatic Resource Counting (ARC). A page in the
goes into further detail:

J2ObjC generates different memory management code, depending on
which method is chosen. By default, it currently uses reference
counting with autorelease pools. Translating with the -use-gc flag,
though, and code that uses garbage collection is created instead.
Finally, there is a –use-arc option to generate code which uses
ARC; when that becomes more standard, it will become the

The project’s
is hosted on Google Code under an Apache License 2.0. If
you have a go with it, drop a comment below with your thoughts.

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