$ sudo apt-get update
$ sudo apt-get install postgresql-9.3-pljava-gcj 

postgresql-9.3-pljava-gcj is installed in your system.

Make ensure the postgresql-9.3-pljava-gcj package were installed using the commands given below,

$ sudo dpkg-query -l | grep postgresql-9.3-pljava-gcj *

You will get with postgresql-9.3-pljava-gcj package name, version, architecture and description in a table

postgresql-9.3-pljava-gcj package basic information: