code: private void initializePrefixes()
  	{
  		if (namespaceMap == null) {
  			// TODO use logger
  			System.err
  					.println("Cannot use whitespace filter without initializing the namespace-prefix map for the current Wikipedia language version. DISABLING FILTER.");
  		}
  		else {
  			prefixesToAllow = new HashSet<String>();
  			prefixesToReject = new HashSet<String>();
  
  			for (Entry<Integer, String> namespace : namespaceMap.entrySet()) {
  				if (allowedNamespaces.contains(namespace.getKey())) {
  					prefixesToAllow.add(namespace.getValue() + ":");
  				}
  				else {
  					prefixesToReject.add(namespace.getValue() + ":");
  				}
  			}
  		}
  	}
docs: Initialize allowed and restricted prefixes