GJDB is a modification of JDB, a debugger that comes with the public JDK (Java Development Kit) from Sun. This modification comes with an ELisp file that allows easy use with the FSF Emacs debugging interface. Unlike Sun's version, it also allows you to debug programs that take input from the terminal (that is, from standard input: System.in in Java terms). The expression language has been extended to include much more of the language (including numerous features missing from jdb, such as array allocation, initialized array allocation, the .super operator, less fussy overload resolution, and numerous binary numeric and logical operations). The current version runs on (at least) Linux, Solaris, and MacOS X.
The current version runs with JDK versions 1.3--1.5 of the JDK. I distribute gjdb as a compressed tarball, which you can download by shift-clicking from the appropriate gjdb-* file in the archive. Unpack with a command such as
gunzip -c gjdb-6.2.2.tgz | tar xf -or (with GNU tar):
tar xzf gjdb-6.2.2.tgzand then read the README file.