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.
/usr/java/j2sdk1.4.1/ 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.