The '''GNU Compiler for Java''' (a.k.a. '''GCJ''' or '''gcj''') is a free software compiler for the Java programming language and a part of the GNU Compiler Collection.

GCJ 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 JARs containing such files into machine code.