look here
https://stackoverflow.com/questions/6477415/how-to-set-oracles-java-as-the-default-java-in-ubuntu
not the accepted answer but Barracuda's, which I reproduce below:
to set Oracle's Java SE Development Kit as the system default Java
just download the latest Java SE Development Kit from [here][1] then
create a directory somewhere you like in your file system for example
/usr/java
now extract the files you just downloaded in that
directory:
$ sudo tar xvzf jdk-8u5-linux-i586.tar.gz -C /usr/java
now to set your JAVA_HOME
environment variable:
$ JAVA_HOME=/usr/java/jdk1.8.0_05/
$ sudo update-alternatives --install /usr/bin/java java ${JAVA_HOME%*/}/bin/java 20000
$ sudo update-alternatives --install /usr/bin/javac javac ${JAVA_HOME%*/}/bin/javac 20000
make sure the Oracle's java is set as default java by:
$ update-alternatives --config java
you get something like this:
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /opt/java/jdk1.8.0_05/bin/java 20000 auto mode
1 /opt/java/jdk1.8.0_05/bin/java 20000 manual mode
2 /usr/lib/jvm/java-6-openjdk-i386/jre/bin/java 1061 manual mode
Press enter to keep the current choice[*], or type selection number:
pay attention to the asterisk before the numbers on the left and if
the correct one is not set choose the correct one by typing the number
of it and pressing enter. now test your java:
$ java -version
if you get something like the following, you are good to go:
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) Server VM (build 25.5-b02, mixed mode)
also note that you might need root permission or be in sudoers group
to be able to do this. I've tested this solution on both ubuntu 12.04
and Debian wheezy and it works in both of them.
[1]:
http://www.oracle.com/technetwork/java/javase/downloads/index.html