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Stanford CoreNLP provides a set of natural language analysis tools which can take raw English language text input and give the base forms of words, their parts of speech, whether they are names of companies, people, etc., normalize dates, times, and numeric quantities, mark up the structure of sentences in terms of phrases and word dependencies, and indicate which noun phrases refer to the same entities. It provides the foundational building blocks for higher level text understanding applications.

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package edu.stanford.nlp.trees;

import edu.stanford.nlp.ling.Label;

/**
 * A Span is an optimized SimpleConstituent object.
 * It provides exactly the same functionality as a SimpleConstituent, but
 * by being final, and with its own implementation of Span equality,
 * it runs faster, so as to placate Dan Klein.  (With JDK1.3 client, it still
 * doesn't run as fast as an implementation outside of the SimpleConstituent
 * hierarchy, but with JDK1.3 server, it does!  And both versions are
 * several times faster with -server than -client, so that should be used.)
 *
 * @author Christopher Manning
 * @version 2001/01/08
 */
public final class Span extends SimpleConstituent {

  /**
   * Create an empty Span object.
   */
  public Span() {
    // implicitly super();
  }


  /**
   * Create a Span object with given values.
   *
   * @param start start node of edge
   * @param end   end node of edge
   */
  public Span(int start, int end) {
    super(start, end);
  }


  /**
   * An overloading for efficiency for when you know that you're comparing
   * with a Span.
   *
   * @param sp the span to compare against
   * @return whether they have the same start and end
   * @see Constituent#equals(Object)
   */
  public boolean equals(final Span sp) {
    return start() == sp.start() && end() == sp.end();
  }


  // extra class guarantees correct lazy loading (Bloch p.194)
  private static class ConstituentFactoryHolder {

    private ConstituentFactoryHolder() {}  // static holder class


    /**
     * A SpanFactory acts as a factory for creating objects
     * of class Span.
     * An interface.
     */
    private static class SpanFactory implements ConstituentFactory {

      public Constituent newConstituent(int start, int end) {
        return new Span(start, end);
      }


      public Constituent newConstituent(int start, int end, Label label, double score) {
        return new Span(start, end);
      }

    }


    private static final ConstituentFactory cf = new SpanFactory();

  } // end static class ConstituentFactoryHolder


  /**
   * Return a factory for this kind of constituent.
   * The factory returned is always the same one (a singleton).
   *
   * @return The constituent factory
   */
  @Override
  public ConstituentFactory constituentFactory() {
    return ConstituentFactoryHolder.cf;
  }


  /**
   * Return a factory for this kind of constituent.
   * The factory returned is always the same one (a singleton).
   *
   * @return The constituent factory
   */
  public static ConstituentFactory factory() {
    return ConstituentFactoryHolder.cf;
  }

}