code: public int getNumberOfCategorizedArticles(Wikipedia pWiki, CategoryGraph catGraph) throws WikiApiException{
          if (categorizedArticleSet == null) {    // has not been initialized yet
              iterateCategoriesGetArticles(pWiki, catGraph);
          }
          return categorizedArticleSet.size();
      }
docs: If the return value has been already computed, it is returned, else it is computed at retrieval time.
  @param pWiki The wikipedia object.
  @param catGraph The category graph.
  @return The number of categorized articles, i.e. articles that have at least one category.