void
setCount(int field, int value) {
	if (value < 0 || value > 0xFFFF)
		throw new IllegalArgumentException("DNS section count " +
						   value + " is out of range");
	counts[field] = value;
}
Retrieves the mesasge's opcode
@see Opcode
src/main/java/core/org/xbill/DNS/Header.java