code: public void addQuad(final String s, final String p, final String value, final String datatype,
              final String language, String graph) {
          if (graph == null) {
              graph = "@default";
          }
          if (!containsKey(graph)) {
              put(graph, new ArrayList<Quad>());
          }
          ((ArrayList<Quad>) get(graph)).add(new Quad(s, p, value, datatype, language, graph));
      }
docs: Adds a triple to the specified graph of this dataset
  
  @param s
  the subject for the triple
  @param p
  the predicate for the triple
  @param value
  the value of the literal object for the triple
  @param datatype
  the datatype of the literal object for the triple (null values
  will default to xsd:string)
  @param graph
  the graph to add this triple to
  @param language
  the language of the literal object for the triple (or null)