Java compiler

A Java compiler is a compiler for the Java programming language. The most common form of output from a Java compiler is Java class files containing platform-neutral Java bytecode, but there are also compilers that emit optimized native machine code for a particular hardware/operating system combination.

Most Java-to-bytecode compilers, Jikes being a well known exception, do virtually no optimization, leaving this until run time to be done by the JRE.

The Java virtual machine (JVM) loads the class files and either interprets the bytecode or just-in-time compiles it to machine code and then possibly optimizes it using dynamic compilation.

A standard on how to interact with Java compilers programmatically was specified in JSR 199.

Major Java compilers

As of 2012, the following are major Java compilers:

The Java Programming Language Compiler (javac), included in the Java Development Kit from Oracle Corporation, open-sourced since 13 November 2006.
GNU Compiler for Java (GCJ), a part of the GNU Compiler Collection, which compiles C, Fortran, Pascal and other programming languages besides Java. It can also generate native code using the back-end of GCC.
Eclipse Compiler for Java (ECJ), an open source incremental compiler used by the Eclipse project.

↑ Ghosh, Subdipto (2001). Java, Jini Technologies. Proceedings of SPIE--the International Society for Optical Engineering 4521. Society of Photo-Optical Instrumentation Engineers. p. 118. ISBN 9780819442451. Retrieved 2013-07-29. Eck et al. describe the only semantic compressor available for Java, jaccelerator. Jaccelerator, which is similar in principle to SlimBinaries.8 unites a Java compiler, which compiles the Java source code to its syntax tree, and a run-time compiler.

Sun's OpenJDK javac page
JSR 199 Java Compiler API Java Specification Request for invoking the Java compiler from a Java program
A Formal Introduction to the Compilation of Java, Stephan Diehl, "Software - Practice and Experience", Vol. 28(3), pages 297-327, March 1998.