Considering that you have several JVM installed on your Ubuntu box, use the following command to interactively change the default Java flavor you want to run.

sudo update-alternatives --config java

You can then choose the Java alternative you would like /usr/bin/java to point to.

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/java-6-openjdk/jre/bin/java  1061  manual mode
* 2  /usr/lib/jvm/java-6-sun/jre/bin/java      63    manual mode

Press enter to keep the current choice[*], or type selection number: