public String toString() {
        StringBuilder sb = new StringBuilder().append("BucketId(0x");
        String number = Long.toHexString(getId());
        for (int i=number.length(); i<16; ++i) {
            sb.append('0');
        }
        sb.append(number).append(')');
        return sb.toString();
    }
Creates a bucket id with the given raw bucket id. This is a 64 bit mask
where the first 6 MSB bits set how many LSB bits should actually be used.
Right now it only have simple functionality. More will be added for it
to be configurable.
document/src/main/java/com/yahoo/document/BucketId.java