public final void checkOccurrenceNumbers() {
		if (LOGGER_.isTraceEnabled())
			LOGGER_.trace(toString() + " occurences: "
					+ printOccurrenceNumbers());
		if (positiveOccurrenceNo < 0 || negativeOccurrenceNo < 0)
			throw new ElkUnexpectedIndexingException(toString()
					+ " has a negative occurrence: " + printOccurrenceNumbers());
	}
public final void checkOccurrenceNumbers() {
		if (LOGGER_.isTraceEnabled())
			LOGGER_.trace(toString() + " occurences: "
					+ printOccurrenceNumbers());
		if (positiveOccurrenceNo < 0 || negativeOccurrenceNo < 0)
			throw new ElkUnexpectedIndexingException(toString()
					+ " has a negative occurrence: " + printOccurrenceNumbers());
	}
public final void checkOccurrenceNumbers ( ) { if ( LOGGER_ . isTraceEnabled ( ) ) LOGGER_ . trace ( toString ( ) + " occurences: " + printOccurrenceNumbers ( ) ) ; if ( positiveOccurrenceNo < 0 || negativeOccurrenceNo < 0 ) throw new ElkUnexpectedIndexingException ( toString ( ) + " has a negative occurrence: " + printOccurrenceNumbers ( ) ) ; }
verifies that occurrence numbers are not negative
verifies that occurrence numbers are not negative