Note: If you wish to switch back to IcedTea re-run the above  2  alternative commands using  15000  instead of  20000 .

[root@localhost ~]# /usr/sbin/alternatives --install /usr/bin/java java /opt/jre1.6/bin/java 15000
[root@localhost ~]# /usr/sbin/alternatives --install /usr/lib/mozilla/plugins/libjavaplugin.so \
> libjavaplugin.so /opt/jre1. 6 /plugin/i386/ns7/libjavaplugin_oji.so  15000 
[root@localhost ~]# java -version
java version "1.6.0_03"
Java(TM) SE Runtime Environment (build  1 . 6 .0_03-b05)
Java HotSpot(TM) Client VM (build  1 . 6 .0_03-b05, mixed mode, sharing)
[root@localhost ~]#