String
rrToString() {
	StringBuffer sb = new StringBuffer();
	sb.append(preference);
	sb.append(" ");
	sb.append(map822);
	sb.append(" ");
	sb.append(mapX400);
	return sb.toString();
}
Converts the PX Record to a String
src/main/java/core/org/xbill/DNS/PXRecord.java