public void
setRcode(int value) {
	if (value < 0 || value > 0xF)
		throw new IllegalArgumentException("DNS Rcode " + value +
						   " is out of range");
	flags &= ~0xF;
	flags |= value;
}
Sets the message's rcode
@see Rcode
src/main/java/core/org/xbill/DNS/Header.java