code: public synchronized void
  addRRset(RRset rrset, int cred) {
  	long ttl = rrset.getTTL();
  	Name name = rrset.getName();
  	int type = rrset.getType();
  	Element element = findElement(name, type, 0);
  	if (ttl == 0) {
  		if (element != null && element.compareCredibility(cred) <= 0)
  			removeElement(name, type);
  	} else {
  		if (element != null && element.compareCredibility(cred) <= 0)
  			element = null;
  		if (element == null) {
  			CacheRRset crrset;
  			if (rrset instanceof CacheRRset)
  				crrset = (CacheRRset) rrset;
  			else
  				crrset = new CacheRRset(rrset, cred, maxcache);
  			addElement(name, crrset);
  		}
  	}
  }
docs: Adds an RRset to the Cache.
  @param rrset The RRset to be added
  @param cred The credibility of these records
  @see RRset