JAVA

calling activity method from fragment:

((YourActivityClassName)getActivity()).yourPublicMethod();

call fragment method from activity

YourFragmentClass fragment = (YourFragmentClass)fm.findFragmentByTag("yourTag");

fragment call activity

Intent myIntent = new Intent((ParentActivity)getActivity(), YourOtherActivity.class);
(ParentActivity)getActivity().startActivity(myIntent);