@Override
    public String toString() {
        return String.format("%" + MASK_LENGTH + "s", Integer.toBinaryString(this.mask))
                .replace(' ', '0');
    }
Output has mask position zero on the right
stroom-statistics/stroom-statistics-impl-hbase/src/main/java/stroom/statistics/impl/hbase/rollup/RollUpBitMask.java