Recently, I stumbled upon JCGO, an interesting project, which translates Java 1.4 code into C.
In this article, I show how to create a native Windows app out of a small Java app.
The Java app I will use is NetCat (https://github.com/rafalrusin/netcat). You can download precompiled executable, netcat.exe, from https://github.com/rafalrusin/netcat/downloads.
So the first step is to download all dependencies. I will use MinGW, MinGW GCC, jcgo-lib-1_14.tar.gz, jcgo-src-1_14.tar.bz2, classpath-0.93 (http://ftp.gnu.org/gnu/classpath/classpath-0.93.tar.gz) and Java sources for the app with dependent libraries: https://github.com/rafalrusin/netcat, commons cli 1.2 (http://commons.apache.org/cli/download_cli.cgi). You need to put all this in the same directory, so it’ll have structure like this:
auxbin classpath-0.93 commons-cli-1.2-src dlls goclsp src jcgo jcgo.exe jcgo.jar libs miscsrc netcat out rflg_out stdpaths.in
jcgo.exe -sourcepath netcat/src -sourcepath commons-cli-1.2-src/src/java netcat.NetCat @stdpaths.in -d out Initializing... Analysis pass... Output pass... Writing class tables... Creating main file... Parsed: 293 java files (2699 KiB). Analyzed: 3067 methods. Produced: 640 c/h files (3769 KiB). Contains: 1490 java methods, 4119 normal and 288 indirect calls. Done conversion in 1 seconds. Total heap size: 36572 KiB.
gcc -DJCGO_INET -DJCGO_NOFP -DJCGO_WIN32 -DJCGO_THREADS -I src/include/ -I src/include/boehmgc/ -I src/native/ out/Main.c -o netcat.exe libs/x86/mingw/libgcmt.a -lws2_32
$ netcat.exe google.com -p 80 Connecting to google.com port 80 GET HTTP/1.0 302 Found Location: http://www.google.pl/ Cache-Control: private Content-Type: text/html; charset=UTF-8 Set-Cookie: PREF=ID=2f3085ac38771e98:FF=0:TM=1345885031:LM=1345885031:S=8A-IkreMgCogMsey; expires=Mon, 25-Aug-2014 08:57:11 GMT; path=/; domain=.google.com Set-Cookie: NID=63=O_QZ4bDrzYNiiE0DY8RT-34c_pGt_OZagP3gzrzqCAx_Xo2kO7s9zVrUOx7FVz4TyAEY7Wx9UhglYZSX9UHSdzT7c9mUKzfkJFp5lk5FyfiMIcKITLhgSX4__3QwEYBS; expires=Sun , 24-Feb-2013 08:57:11 GMT; path=/; domain=.google.com; HttpOnly P3P: CP="This is not a P3P policy! See http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=151657 for more info." Date: Sat, 25 Aug 2012 08:57:11 GMT Server: gws Content-Length: 218 X-XSS-Protection: 1; mode=block X-Frame-Options: SAMEORIGIN <HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8"> <TITLE>302 Moved</TITLE></HEAD><BODY> <H1>302 Moved</H1> The document has moved <A HREF="http://www.google.pl/">here</A>. </BODY></HTML>
I like the approach of translating Java code into C, because compared to other tools, which generate C++ code, this is more suitable for embedded devices. For example it is possible to generate code for iOS, because Objective C is a superset of C.
One feature I would like to see though is to be able to use reference counting instead of full gc. This is because one of the advantages of C over Java is that it doesn’t have GC hangs. So then the programmer would have to make sure there’s no cycles in orphaned object structure.
Update: Ivan Maidansky, an author of JCGO, has put some interesting comments regarding this article. In particular, he is aware of some apps in Apple Store, which do this kind of translation. Also, reference counting is discouraged due to multithreading issues. These comments can be found here: https://github.com/ivmai/JCGO/issues/2