question: private void checkAxisIndices ( List indices ) { if ( indices == null ) { return ; } int count = indices . size ( ) ; if ( count == 0 ) { throw new IllegalArgumentException ( "Empty list not permitted." ) ; } HashSet set = new HashSet ( ) ; for ( int i = 0 ; i < count ; i ++ ) { Object item = indices . get ( i ) ; if ( ! ( item instanceof Integer ) ) { throw new IllegalArgumentException ( "Indices must be Integer instances." ) ; } if ( set . contains ( item ) ) { throw new IllegalArgumentException ( "Indices must be unique." ) ; } set . add ( item ) ; } }
target:  This method is used to perform argument checking on the list of axis indices passed to mapDatasetToDomainAxes() and mapDatasetToRangeAxes().