Emma is an easy use open source code coverage tool. It has both the on-the-fly and offline instrumenting. Invoking can be done by ant task or command line operations.
I've tried the offline instrumentation with the following commands,
1. Instrument the class
java -cp emma.jar emma instr -m overwrite -cp My.jar
2. Running the application
Placed the emma.jar in the application classpath. Run the tests in the application.
3. Generating report
java -cp emma.jar emma report -r html -in coverage.em,coverage.ec
In order to understand the effectiveness of the code coverage, the following are needed,
1. List of cases/steps/features which are going to be tested
2. List of classes/jars under test which are instrumented
3. Result of the test
4. Coverage report
Read this article to know more about the coverage analysis.