code: public List<ClassDoc> implementingclasses(ClassDoc cd) {
          List<ClassDoc> result = get(implementingclasses, cd);
          List<ClassDoc> subinterfaces = allSubs(cd, false);
  
          //If class x implements a subinterface of cd, then it follows
          //that class x implements cd.
          Iterator<ClassDoc> implementingClassesIter, subInterfacesIter = subinterfaces.listIterator();
          ClassDoc c;
          while(subInterfacesIter.hasNext()){
              implementingClassesIter = implementingclasses(
                      subInterfacesIter.next()).listIterator();
              while(implementingClassesIter.hasNext()){
                  c = implementingClassesIter.next();
                  if(! result.contains(c)){
                      result.add(c);
                  }
              }
          }
          Collections.sort(result);
          return result;
      }
docs: Return the list of classes which implement the interface passed.
  
  @param cd interface whose implementing-classes list is required.