code: public XPathFactory newFactory(String uri) {
          if (uri == null) {
              throw new NullPointerException("uri == null");
          }
          XPathFactory f = _newFactory(uri);
          if (debug) {
              if (f != null) {
                  debugPrintln("factory '" + f.getClass().getName() + "' was found for " + uri);
              } else {
                  debugPrintln("unable to find a factory for " + uri);
              }
          }
          return f;
      }
docs: <p>Creates a new {@link XPathFactory} object for the specified
  schema language.</p>
  
  @param uri
  Identifies the underlying object model.
  
  @return <code>null</code> if the callee fails to create one.
  
  @throws NullPointerException
  If the parameter is null.