code: public synchronized void
  addNegative(Name name, int type, SOARecord soa, int cred) {
  	long ttl = 0;
  	if (soa != null)
  		ttl = soa.getTTL();
  	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)
  			addElement(name, new NegativeElement(name, type,
  							     soa, cred,
  							     maxncache));
  	}
  }
docs: Adds a negative entry to the Cache.
  @param name The name of the negative entry
  @param type The type of the negative entry
  @param soa The SOA record to add to the negative cache entry, or null.
  The negative cache ttl is derived from the SOA.
  @param cred The credibility of the negative entry