$ sudo apt-get update
$ sudo apt-get install gcj-4.9-source 

gcj-4.9-source is installed in your system.

Make ensure the gcj-4.9-source package were installed using the commands given below,

$ sudo dpkg-query -l | grep gcj-4.9-source *

You will get with gcj-4.9-source package name, version, architecture and description in a table

gcj-4.9-source package basic information: