MapR 5.0 Documentation : Java Setup

If Java is already installed, check which versions of Java are installed: java -version
If JDK 6 is installed, the output will include a version number starting with 1.6, and then below that the text Java(TM). Example:

java version "1.6.0_24"
Java(TM) SE Runtime Environment (build 1.6.0_24-b07)

Use update-alternatives to make sure JDK 6 is the default Java: sudo update-alternatives --config java