The Oracle JDK is no longer maintained in the Ubuntu repository, but if you want to install it, there is still a way to install via apt. Per the team:

You can add their repository to apt and install the Oracle Java installer, which verifies your agreement to Oracle's licensing terms and downloads the JDK from Oracle.

sudo add-apt-repository ppa:webupd8team/javasudo
apt-get updatesudo
apt-get install oracle-java7-installer

You can then install another package to automatically set up the Java environment settings.

sudo apt-get install oracle-java7-set-default

More details, such as automating the Oracle license acceptance, at the post.