Afaik j2sdk1.4.2 is inside /usr/lib/java, so some might also put other new release there like /usr/lib/java/j2sdk1.4.3. I've j2sdk1.4.1.3 also on the redhat partition, but in /usr/java.
The PATH should be something like:
export JAVA_HOME=/usr/lib/java/j2sdk1.4.2
export PATH=$PATH:$JAVA_HOME/bin
export MANPATH=$MANPATH:$JAVA_HOME/man
Install also java plugin for mozilla n netscape
$ cd /usr/lib/mozilla-1.4/plugins
ln -s /usr/java/j2sdk1.4.2/jre/plugin/i386/ns610-gcc32/libjavaplugin_oji.so .
$ cd /usr/lib/netscape/plugins
ln -s /usr/java/j2sdk1.4.2/jre/plugin/i386/ns610-gcc32/libjavaplugin_oji.so .
Restart netscape/moz, click help -> about plug-ins, u should also see the many java plugins there ..
Last tip:
Googling("plugger") install also plugger for moz/netscape .. Then u can have more browser experience ..