The Oracle JDK is targeted more towards an enterprise audience which values stability. It's based on one of the OpenJDK releases but is then given long term support (LTS).
OpenJDK will have a feature release every 6 months which is only supported until the next feature release. It's essentially a continuous stream of releases targeted to developers.
Below are steps to install Oracle JDK on Ubuntu 16.04
Step 1: Add Oracle PPA
$ sudo add-apt-repository ppa:webupd8team/java
Step 2: Update your package repository
$ sudo apt-get update
Step 3: Install Oracle JDK 9
$ sudo apt-get install oracle-java9-installer
Step 4: Verify Java Installed
$ javac -version