To move back and forth between a JDK 1.1.n and the J2SDK v 1.2.1, you must change the PATH environment variable:
To switch to using J2SDK v 1.2.1, place directory /usr/opt/java121/bin first in your PATH. This is the directory that contains the J2SDK v 1.2.1 executables. For example, using csh(1):
setenv PATH /usr/opt/java121/bin:$PATH
To switch back to using the 1.1.n version, remove the above directory from your PATH. This is important, both versions are installed because the old version is necessary for some existing software.
JWW note: you can do this on the fly with the command above without actually editing your path.