listeners.addElement(listener);
listeners.add(listener);
    void addListener(DNSListener listener, DNSQuestion question) {        long now = System.currentTimeMillis();                // add the new listener        listeners.addElement(listener);                // report existing matched records        if (question != null) {            for (DNSCache.CacheNode i = cache.find(question.name); i != null; i = i.next()) {                DNSRecord c = (DNSRecord) i.getValue();                if (question.answeredBy(c) && !c.isExpired(now)) {                    listener.updateRecord(this, now, c);                }            }        }    }