private int getNextDataUsageIndex() throws PropertyException {
        Set<Integer> usedIndexes = getDataUsageNameIndexes();
        int nextIndex = 1;
        while (usedIndexes.contains(nextIndex)) {
            nextIndex++;
        }
        return nextIndex;
    }
private int getNextDataUsageIndex ( ) throws PropertyException { Set < Integer > usedIndexes = getDataUsageNameIndexes ( ) ; int nextIndex = 1 ; while ( usedIndexes . contains ( nextIndex ) ) { nextIndex ++ ; } return nextIndex ; }
Returns the lowest unused index for data usage names.<br>
Data usage names are enumerated (DATA_USAGE_1, DATA_USAGE_2, ...).<br>
When new data usages are added, the lowest unused index is used as
property name.

@return The lowest free index to be used for data usage naming.
@throws PropertyException if the extraction of used indexes fails.
@see #getDataUsageNameIndexes()