Useful little nugget obtained from Ubuntu help pages:
Choosing the default Java to use
If your system has more than one version of Java, configure which one your system uses by entering the following command in a terminal window
sudo update-alternatives --config java
This will present you with a selection that looks similar to the following (the details may differ for you):
There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ———————————————————— * 0 /usr/lib/jvm/java-6-openjdk/jre/bin/java 1061 auto mode 1 /usr/lib/jvm/jre1.7.0/jre/bin/java 3 manual mode Press enter to keep the current choice[*], or type selection number: 1
