Hi Pengcheng:

http://www.ccs.neu.edu/research/demeter/demeter-method/LawOfDemeter/object-formulation.html

describes the object form of the Law of Demeter.

Please can you also allow the collection case.

See:
/proj/adaptive/www/demeter-method/LawOfDemeter/check-with-AspectJ/demeterj-test-simple/gen

for an example where your checker fails.

-- Karl