Why is alternatives command used when installing Java on a Linux machine

Question

The below command is need when installing Java on a Linux machine (saw the command in a tutorial).

alternatives --install /usr/bin/java java /usr/java/jre1.         


        

Answer 1

To address what the 20000 is for, this is the priority for that particular alternative. Per the man page:

Each alternative has a priority associated with it. When a link group is in automatic mode, the alternatives pointed to by members of the group will be those which have the highest priority.