How Do I Setup JDK and Maven on Ubuntu 14.04 LTS?

The "trusty" maven package pulls in openjdk-7-jre-headless. Install it using:

sudo apt-get install maven  

Add the Java 7 JDK:

sudo apt-get install openjdk-7-jdk  

Java 8 is newer than "trusty", so it needs to be taken from a backport:

sudo apt-get install software-properties-common  
sudo add-apt-repository -y ppa:openjdk-r/ppa  
sudo apt-get update  
sudo apt-get install -y openjdk-8-jdk  

Switch between Java 7 and Java 8:

update-alternatives --list javac  

Shows:

/usr/lib/jvm/java-7-openjdk-amd64/bin/javac
/usr/lib/jvm/java-8-openjdk-amd64/bin/javac

Switch to Java 7:

sudo update-alternatives --set javac $(update-alternatives --list javac | grep java-7)