J2c Save

Introduction

J2C will convert Java code into hopefully compilable C++(11) code. It works on source level, translating Java source code constructs into their rough equivalents in C++ . The output will be reasonably valid C++ code that looks a lot like its Java counterpart and hopefully works mostly the same.

The translation is based on The Java Language Specification, Third Edition, by Gosling, James and Joy, Bill and Steele, Guy and Bracha, Gilad (that's Java 1.6). The translated code should be valid as specified by the ISO/IEC 14882:2011 C++ standard (or C++11 as the rest of the world knows it).

The generated code won't work out of the box - you need to remove or implement dependencies such as the JRE.

Status

This project is an idea I've been wanting to try out written down in code. Think of it as a paper napkin with some notes on, but in this case, the notes compile and sometimes spit out working stuff. In other words, no guarantees and no quality control label.

That said, j2c successfully converts most of OpenJDK 6 and SWT 3.7 to C++ that compiles and passes a quick ocular inspection. Most language features of Java 1.6 are covered (i e you'll still need a JDK and runtime).

With a few patches and implementations of native methods in the converted OpenJDK code, the included Hello test prints it's message. A more complete example would need a more complete runtime, either by implementing the native and JVM parts of a class library or by implementing the stubs that are generated for missing dependencies.

This is the first time I write an Eclipse plugin, so be nice.

Install / Run

J2C comes in the form of an Eclipse plugin. You need at least Eclipse 3.8+ and Java 1.6+ to run this plugin!

The most recent version of the project is available as source code. You can get it either from Bitbucket (https://bitbucket.org/arnetheduck/j2c/) or github (https://github.com/arnetheduck/j2c).

From time to time, a release may appear at the Bitbucket site - see https://bitbucket.org/arnetheduck/j2c/downloads . About that same time, the update site (https://bitbucket.org/arnetheduck/j2c.site/raw/default/) should be updated.

If you installed via site, it should just work.

If you downloaded the jar, copy it to $ECLIPSE_HOME/dropins.

If you downloaded the source code you'll have run the plugin by opening the project in Eclipse and starting a new Eclipse test instance by using the run button in the plugin.xml overview.

Once you have the plugin running, set up your Java code as a Java Project. Eclipse must be able to compile your code for J2C do to its work!

Once the Java Project is set up (with all dependencies etc), you can run J2C by right-clicking the project (or a class/package) in the 'Project Explorer' or 'Package Explorer' view and choosing the 'Translate to C++' option. You will need to create a folder for the conversion output - the plugin will tell you where.

The generated code will contain references to your JRE (stuff from the java.* packages), as well as some generic helpers. The JRE dependencies will likely be stubbed out in the ext folder in the generated code, and trivial, non-working implementations of the rest can be found in j2c.cpp. You'll need to supplant the converted code with implementations of all JRE features you're using, or replace them manually to use equivalents from C++ libraries such as STL.

Testing

The test project contains a few cases which should be handled correctly by the translator (by correctly, I mean that they compile with g++ 4.7). You'll find a CDT project in ctest that builds using the generated Makefile after running the plugin on the test project.

Output

For each Java class, j2c will output a header file and its implementation. Inner classes end up in separate .h/.cpp pairs. Native method stubs will be put in a separate file for your editing pleasure.

Classes for which there is no source will have a header written as well as a stub file with empty implementations. Throughout, the heap will be used to allocate class instances but no attempt is made to collect garbage - I recommend Boehm's garbage collector for that.

What's missing (that I can think of right now)

• Reflection
• Anything involving byte code (class loading, dynamic code generation, etc)
• Command line support / build integration

Helping out

Patches and forks are most welcome, as is testing, but please don't report issues unless you also attach a simple test case.

Final words

Send me a note if you manage (or not) to do something useful with this converter!

Licensing

The project is licensed under the Eclipse Public License 1.0.

Thanks

No animals were hurt while writing this code, but the Nightwatchman might have sore fingers and throat from all that playing...

Have fun, Jacek Sieka (arnetheduck using google mail point com)