public String
	toString() {
		StringBuffer sb = new StringBuffer();
		if (type == 0)
			sb.append("NXDOMAIN " + name);
		else
			sb.append("NXRRSET " + name + " " + Type.string(type));
		sb.append(" cl = ");
		sb.append(credibility);
		return sb.toString();
	}
A cache of DNS records.  The cache obeys TTLs, so items are purged after
their validity period is complete.  Negative answers are cached, to
avoid repeated failed DNS queries.  The credibility of each RRset is
maintained, so that more credible records replace less credible records,
and lookups can specify the minimum credibility of data they are requesting.
@see RRset
@see Credibility

@author Brian Wellington
src/main/java/core/org/xbill/DNS/Cache.java