Interface classes often extend existing XQJ interface classes and do not break the XQJ Specification, for instance XQConnection2 simply extends XQConnection, so the user of an XQJ implementation can only make use of XQJ2 features by explicitly casting a standard XQJ object into an XQJ2 instance which has everything the previous instance had and more, for instance:

  XQConnection xqc = xqds.getConnection();
  XQConnection2 xqc2 = (XQConnection2)conn;

  // or quicker approach ...

  XQConnection2 conn = (XQConnection2)xqds.getConnection();

Despite the XQJ2 API being experimental, effort has been made to keep different versions of XQJ2 compatible between releases.