code: public static Class<?>[] getAggregateIdClasses(Class<? extends AggregateRoot<?>>[] aggregateRootClasses) {
          checkNotNull(aggregateRootClasses, "aggregateRootClasses should not be null");
          Class<?>[] result = new Class<?>[aggregateRootClasses.length];
          for (int i = 0; i < aggregateRootClasses.length; i++) {
              result[i] = resolveGenerics(AggregateRoot.class, aggregateRootClasses[i])[0];
          }
          return result;
      }
docs: Returns an arrays of all identifier class corresponding the the given array of aggregate root
  classes.