Compile this project against Autoplot, for example:
wget -N https://autoplot.org/latest/autoplot.jar
/usr/local/jdk1.8/bin/javac -cp autoplot.jar apextension/Extension.java # Note newer Javas don't like this jar
jar tvf /tmp/APExtension.jar apextension/Extension.class
Then this can be imported into an Autoplot script with:
import sys
sys.path.append("/tmp/APExtension.jar")
from apextension import Extension
print Extension.total( 3,4 )