See the Javadocs in <EPM_ORACLE_HOME>/common/docs/ReportingAnalysis/SDK/javadoc.
This interface is returned from search methods supported by the Query interface. QueryVector provides access functions that enables your program to recover elements returned from the search method invocation. The interface enables the program to discover the number of elements returned by the search, to determine whether the returned element list is empty, to access each element in the QueryVector interface by a numeric index value, or to obtain an Enumeration interface for more comprehensive manipulation of the artifact sets returned by the search request.