From LQWiki

GCJ, the GNU compiler for Java, is part of GCC. It's not a JVM -- instead, gcj is an optimizing "ahead-of-time" compiler, which can compile Java source code (or bytecode if need be) right down to native machine language. It also comes with libgcj which implements the Java runtime as well as the core Java class libraries. Note that developers are currently in the process of merging libgcj with Classpath.

The benefits of using GCJ rather than a JVM are:

• faster startup time
• less memory consumption
• faster program execution

The disadvantages are:

• hardly any java program works

See also

• GCJ homepage
• GNU: Compiling with GCJ
• Compiling Java with GCJ