From http://stackoverflow.com/questions/6477415/how-to-set-oracles-java-as-the-default-java-in-ubuntu

Ubuntu JAVA_HOME config

extract the files you just downloaded in that directory:

$ sudo tar xvzf jdk-8u5-linux-i586.tar.gz -C /usr/java

***[if folder notfound (/usr/java) then Command: sudo mkdir /usr/java]

now to set your JAVA_HOME environment variable:

$ export 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:

$ sudo update-alternatives --config java



you get something like this:

There is only one alternative in link group java (providing /usr/bin/java): /usr/java/jdk1.8.0_25/bin/java
Nothing to configure.

Or,
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:

$ 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)

Got it on Ubuntu 14.04LTE

extract android studio file
goto extracted directory and /bin directory (i.e. android-studio/bin)
then in terminal run command:
$ ./studio.sh