Cobertura is a free and open-source Java tool based on jcoverage that calculates the percentage of code and branches covered by tests.
EMMA is an open-source toolkit that measures and reports the percentage of Java code covered by unit tests.
"However cobertura looks more modern active last update from 2010 instead of 2005 and generates nicer reports so i would prefer it over emma"
from question "Why is Cobertura not working in my Spring/Hibernate Webapp?"
"If you re going to stick with maven and want a plugin for maven that will do the code-coverage job i think cobertura is a better choice as emma stable last build is from 2005"
from question "How to get code coverage in Android using Maven (android-maven-plugin)"