code: private boolean isImplementationOf(JavaClass cls, JavaClass inf) {
          try {
              if (cls == null) {
                  return false;
              }
              if (cls.implementationOf(inf)) {
                  return true;
              }
          } catch (ClassNotFoundException cnfe) {
              bugReporter.reportMissingClass(cnfe);
          }
          return false;
      }
docs: returns whether the class implements the interface
  
  @param cls
  the class
  @param inf
  the interface to check
  @return if the class implements the interface