Collector

/**
 * <p>Expert: Collectors are primarily meant to be used to
 * gather raw results from a search, and implement sorting
 * or custom result filtering, collation, etc. </p>
 *
 * <p>Lucene's core collectors are derived from {@link Collector}
 * and {@link SimpleCollector}. Likely your application can
 * use one of these classes, or subclass {@link TopDocsCollector},
 * instead of implementing Collector directly:
 *
 * <ul>
 *
 *   <li>{@link TopDocsCollector} is an abstract base class
 *   that assumes you will retrieve the top N docs,
 *   according to some criteria, after collection is
 *   done.  </li>
 *
 *   <li>{@link TopScoreDocCollector} is a concrete subclass
 *   {@link TopDocsCollector} and sorts according to score +
 *   docID.  This is used internally by the {@link
 *   IndexSearcher} search methods that do not take an
 *   explicit {@link Sort}. It is likely the most frequently
 *   used collector.</li>
 *
 *   <li>{@link TopFieldCollector} subclasses {@link
 *   TopDocsCollector} and sorts according to a specified
 *   {@link Sort} object (sort by field).  This is used
 *   internally by the {@link IndexSearcher} search methods
 *   that take an explicit {@link Sort}.

　　

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