The Java directory structure and the search path

Again, assuming you're working with Sun's latest JDK, it's worth knowing at least a portion of the directory structure of what gets installed, provided you didn't do anything out of the ordinary.

                     bin/             binaries (java, javac, etc.)
                     jre/lib/         bootstrap classes
                            ext/      extension classes

Once you know this directory structure, it's a simple matter to make sure that the directory /usr/java/j2sdk1.4.1/bin is added to your search path, either personally or having the administrator do that in /etc/profile.