J% - An Extensible Java Compiler
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J% - An Extensible Java Compiler


J% (pronounced j-mod) is a DSL-aware (Domain-Specific Language) extension of the Java programming language. The prototype implementation consists of a preprocessor, which translates the J% source code to Java compatible code and finally compiles it, through javac to Java bytecode.

So far, it facilitates existing Java DSL APIs, like JDBC for SQL. But this is optional, a module can literally translate DSL code to the host language, since with J% any DSL can be easily integrated into the compiler infrastructure, act as a module and be initialized when needed. For more information visit the website.


  • Static typing The compilation process is type-safe. The compiler is able to perform static typing in one or many DSLs.
  • DSL Syntax Validation The DSL is syntactically checked at compile time and all errors are reported at compile-time.
  • DSL Syntax Each hosted DSL retains its syntax. There is only a minor addition to each DSL grammar of each language to support type mapping with J%.
  • Modular Design Developers can create their own DSLs module through a well-defined API. This way J% can include as many DSLs as needed.
  • Pragmatic Many meta-programming and language extensions deal with language inter-mixture by sacrificing simplicity in the host-language syntax. Other approaches define new languages, which translate the DSLs to the host languages. J% is a pragmatic approach that extends a mainstream language, like Java, and its purpose is to achieve integration with elegance and usage of current DSL application library implementations.


J% consists of a compiler (jmodc), which can be used to compile the source code.

$ jmodc
J% (aka J-mod) compiler
Vassilios Karakoidas (bkarak@aueb.gr)
website: http://bkarak.wizhut.com/projects/jmod

No options are given
jmod compiler usage:
jmod [switches] [files]

-cc, --compiler-context : Prints current compiler context
-st, --symbol-table : Export Symbol Table
-h, --help : Displays help information
-pextc, --print-external-context : Print the External context for each module call
-i, --input-dir : Input source directories. use: input-dir1,input-dir2,...
-cl, --compiler-list : Prints the available compiler list (back-ends)
-am, --add-modules : Add thirs party external modules
-wd, --work-dir : Define the working directory
-pc, --print-classpath : Prints current classpath
-mc, --metrics : Calculate basic metrics set of metrics
-xml, --output-xml : Compiler output is set in XML
-uext, --user-external : Print user-defined external type list
-uexth, --user-external-helper : Print user-defined constructor helper
-ml, --module-list : Prints the available External modules


Several ported applications and several other experinments with can be found in jmod-ports repository.


  • Vassilios Karakoidas, Diomidis Spinellis, J%: Integrating Domain Specific Languages with Java, in Proceedings of 13th Panhelenic Conference on Informatics (PCI 2009), pp. 109-113, 2009. Download