Java compiler

In computing, 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. There exist also compilers emitting 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 runtime to be done by the JRE^{[citation needed]}.

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.

The very first Java compiler developed by Sun Microsystems was written in C using some libraries from C++.^{[citation needed]}

[edit] Major Java compilers

As of 2006, the following are major Java compilers:

javac, included in JDK from Sun Microsystems, open-sourced since 13 November 2006.
GCJ, a part of gcc which compiles C, Fortran, Pascal and other programming languages besides Java. It can also generate native code using the back-end of gcc.
ECJ, the Eclipse Compiler for Java, is an open source incremental compiler used by the Eclipse JDT.
Jikes, an open source compiler from IBM, which is written in C++ and uses a variant of static single assignment form for optimization. As of early 2007 the project is no longer being actively developed ^[1].
JavaNativeCompiler(JNC) is a graphical front-end to GCJ, producing Windows and Linux binary executables.
Excelsior JET (commercial) also compiles Java to Windows and Linux binary executables and packages them for deployment.