# Here are the steps to install Oracle JDK and make if default jvm
# go download the JDK from Oracle, then unpack
tar xzvf ~/Downloads/jdk-7u25-linux-x64.tar.gz
# make jvm directory, if necessary
sudo mkdir /usr/lib/jvm
# move the JDK there
sudo mv jdk1.7.0_25/ /usr/lib/jvm/
# set permissions
sudo chmod a+x /usr/bin/java
sudo chmod a+x /usr/bin/javac
sudo chmod a+x /usr/bin/javaws
sudo chown -R root:root /usr/lib/jvm/jdk1.7.0
# install with update-alternatives
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_25/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_25/bin/javac 1
sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/jdk1.7.0_25/bin/javaws 1
# select the oracle java version for each command below
sudo update-alternatives --config java
sudo update-alternatives --config javac
sudo update-alternatives --config javaws
# make sure it worked
java -version
# make it work in firefox plugin
sudo ln -s /usr/lib/jvm/jdk1.7.0/jre/lib/amd64/libnpjp2.so ~/.mozilla/plugins/
# N.B. you can link libnpjp2.so to /usr/lib/firefox/plugins/ for a system wide installation
# Src: http://askubuntu.com/questions/55848/how-do-i-install-oracle-java-jdk-7
