Introduction

This page is based on experience of setting up Java 8 on Ubuntu 14.04.  Much of it may be applicable to other Java versions and distros.

Architecture

First we check which architecture we are running on.

Open a terminal and type the command :

arch

The output could be i686 or i386 for a 32 bits system or x86_64 for a 64 bits system.

Environment

On Ubuntu 14.04 and for historical reasons the Java commands are under the /usr/bin directory.

However in order to manage multiple version of Java the update-alternatives mechanism has been introduced. It allows multiple "providers" to be installed on the same machine, and configures which is the default. 

This mechanism consists of two directories, /etc/alternatives who contains the symlinks and /var/lib/dpkg/alternatives who contains update-alternatives state information.

Let's see the java command:

xavier@blueberry:/usr/bin$ ls -al /usr/bin/java
lrwxrwxrwx 1 root root 22 Mar 12 2013 /usr/bin/java -> /etc/alternatives/java