There are a number of resources for gcj, including
The gcj home page.[16]
[16] http://gcc.gnu.org/java/
The gcj FAQ.[17]
[17] http://gcc.gnu.org/java/faq.html
The gcj documentation page.[18]
[18] http://gcc.gnu.org/java/docs.html
The JDK1.4 to libgcj comparison page.[19] This resource is particularly useful in deciding whether gcj is an appropriate tool for compiling your program.
[19] http://gcc.gnu.org/java/jdk14-libgcj.html
Many features of gcj are, in fact, "inherited" from the parent project, the GNU Compiler Collection. You can find your way to a lot of good information from the GCC home page.[20]