public static synchronized Cache
getDefaultCache(int dclass) {
	DClass.check(dclass);
	Cache c = (Cache) defaultCaches.get(Mnemonic.toInteger(dclass));
	if (c == null) {
		c = new Cache(dclass);
		defaultCaches.put(Mnemonic.toInteger(dclass), c);
	}
	return c;
}
Gets the Cache that will be used as the default for the specified
class by future Lookups.
@param dclass The class whose cache is being retrieved.
@return The default cache for the specified class.
src/main/java/core/org/xbill/DNS/Lookup.java