JDK8

Be sure to have Java installed already - http://wylbur.us/2015-06-08-installing-jdk8-on-xubuntu

Now install the JDK toolkit - http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2...

Run the install, and make the symlinks to the files

cd Downloads
sudo mkdir -p /opt/java
sudo tar -zxf jdk-7*.tar.gz -C /opt/java
ls /opt/java
sudo ln -sf /opt/java/jdk1.7.0_60 /opt/java/jdk
ls /opt/java/jdk

SQL Developer

Download the tool here: http://www.oracle.com/technetwork/developer-tools/sql-developer/download...

To complete the install, you will also need to install Alien, so that you can install RPM packages in Xubuntu.

sudo apt-get install alien

Install and set the environmental variables for the install. 

cd Downloads
ls sqldev*
sudo alien -ic sqldeveloper-4.0.2.15.21-1.noarch.rpm
ls /opt/sqldeveloper
ls -l $(which sqldeveloper)
a=$(which sqldeveloper)
ls -l /opt/java/jdk
sudo sed -i "1 i unset GNOME_DESKTOP_SESSION_ID" $a
sudo sed -i "1 i export JAVA_HOME=/opt/java/jdk" $a
cat $a

The first time through, use the command line so you can set path variables for the install

sqldeveloper

Resources

https://community.oracle.com/docs/DOC-888316

https://help.ubuntu.com/community/RPM/AlienHowto