GNU Compiler for Java

The GNU Compiler for Java (GCJ) is a compiler for the Java programming language that is part of the GNU Compiler Collection (GCC). It can compile Java source code to either Java Virtual Machine bytecode, or directly to machine code for any of a number of CPU architectures. It can also compile class files containing bytecode or entire Java archives (JARs) containing such class files into machine code. Almost all of the runtime library used by GCJ comes from the GNU Classpath project.

CNI (Compiled Native Interface)

The Compiled Native Interface (CNI) is a software framework for the GNU GCJ compiler which allows Java code to call and be called by native applications (programs specific to a hardware and operating system platform) and libraries written in C++.

It is similar to the Java Native Interface (JNI) framework which comes as standard with various Java virtual machines. However the CNI authors claim various advantages over JNI: [1]

We use CNI because we think it is a better solution, especially for a Java implementation that is based on the idea that Java is just another programming language that can be implemented using standard compilation techniques. Given that, and the idea that languages implemented using Gcc should be compatible where it makes sense, it follows that the Java calling convention should be as similar as practical to that used for other languages, especially C++, since we can think of Java as a subset of C++. CNI is just a set of helper functions and conventions built on the idea that C++ and Java have the *same* calling convention and object layout; they are binary compatible. (This is a simplification, but close enough.)

See also

• GIJ
• GNU Classpath
• Kaffe
• SableVM
• Jikes

External links

• GCJ Homepage
• GCJ Manual
• http://gcc.gnu.org/onlinedocs/gcj/About-CNI.html - 'About CNI' section of GCJ Manual
• http://gcc.gnu.org/java/faq.html - GCJ Frequently Asked Questions