Stemmer.java

package org.basex.util.ft;

import java.util.Collections;
import java.util.LinkedList;

import org.basex.util.Util;

/**
 * Implementation of common stemmer methods.
 *
 * @author BaseX Team 2005-12, BSD License
 * @author Dimitar Popov
 */
public abstract class Stemmer extends LanguageImpl {
  /** List of available stemmers. */
  static final LinkedList<Stemmer> IMPL = new LinkedList<Stemmer>();

  /** Load stemmers and order them by precedence. */
  static {
    // built-in stemmers
    IMPL.add(new EnglishStemmer(null));
    IMPL.add(new GermanStemmer(null));
    IMPL.add(new DummyStemmer(null));

    if(SnowballStemmer.available()) IMPL.add(new SnowballStemmer());
    if(LuceneStemmer.available()) IMPL.add(new LuceneStemmer());
    if(WordnetStemmer.available()) IMPL.add(new WordnetStemmer());

    // sort stemmers and tokenizers by precedence
    Collections.sort(IMPL);
  }

  /** Full-text iterator. */
  private final FTIterator iter;

  /**
   * Constructor.
   */
  Stemmer() {
    this(null);
  }

  /**
   * Constructor.
   * @param ft full-text iterator.
   */
  Stemmer(final FTIterator ft) {
    iter = ft;
  }

  /**
   * Checks if the language is supported by the available stemmers.
   * @param l language to be found
   * @return result of check
   */
  public static boolean supportFor(final Language l) {
    for(final Stemmer s : IMPL) if(s.supports(l)) return true;
    return false;
  }

  /**
   * Factory method.
   * @param l language
   * @param fti full-text iterator
   * @return stemmer
   */
  abstract Stemmer get(final Language l, final FTIterator fti);

  /**
   * Stems a word.
   * @param word input word to stem
   * @return the stem of the word
   */
  protected abstract byte[] stem(final byte[] word);

  @Override
  public final Stemmer init(final byte[] txt) {
    iter.init(txt);
    return this;
  }

  @Override
  public final boolean hasNext() {
    return iter.hasNext();
  }

  @Override
  public final FTSpan next() {
    final FTSpan s = iter.next();
    s.text = stem(s.text);
    return s;
  }

  @Override
  public final byte[] nextToken() {
    return stem(iter.nextToken());
  }

  @Override
  public String toString() {
    return Util.name(this).replace("Stemmer", "");
  }
}