public Ranker create(RankerType ranker) {
			switch (ranker) {
			case CONJUNCTIVE:
				return new RankerConjunctive(indexer);
			case FAVORITE:
			case COSINE:
				return new CosineRanker(indexer);
			case QL:
				return new QLRanker(indexer);
			case PHRASE:
				return new PhraseRanker(indexer);
			case LINEAR:
				return new LinearRanker(indexer);
			case NUMVIEWS:
				return new NumViewsRanker(indexer);
			case FULLSCAN:
			case NONE:
				return new SimpleRanker(indexer);
			default:
				// Do nothing.
			}
			throw new IllegalArgumentException("Unrecognized ranker type:  "
					+ ranker);
		}