org.apache.lucene.search.spell

## Class SpellChecker

- java.lang.Object
- - org.apache.lucene.search.spell.SpellChecker

- All Implemented Interfaces:
    Closeable, AutoCloseable

      public class SpellChecker
      extends Object
      implements Closeable

  Spell Checker class (Main class).
  (initially inspired by the David Spencer code).

  Example Usage:

        SpellChecker spellchecker = new SpellChecker(spellIndexDirectory);
        // To index a field of a user index:
        spellchecker.indexDictionary(new LuceneDictionary(my_lucene_reader, a_field));
        // To index a file containing words:
        spellchecker.indexDictionary(new PlainTextDictionary(new File("myfile.txt")));
        String[] suggestions = spellchecker.suggestSimilar("misspelt", 5);

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static float` | `DEFAULT_ACCURACY` The default minimum score to use, if not specified by calling `setAccuracy(float)` .
    `static String` | `F_WORD` Field name for each word in the ngram index.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SpellChecker(Directory spellIndex)` Use the given directory as a spell checker index with a `LevenshteinDistance` as the default `StringDistance`.
    `SpellChecker(Directory spellIndex, StringDistance sd)` Use the given directory as a spell checker index.
    `SpellChecker(Directory spellIndex, StringDistance sd, Comparator<SuggestWord> comparator)` Use the given directory as a spell checker index with the given `StringDistance` measure and the given `Comparator` for sorting the results.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `clearIndex()` Removes all terms from the spell check index.
    `void` | `close()` Close the IndexSearcher used by this SpellChecker
    `boolean` | `exist(String word)` Check whether the word exists in the index.
    `float` | `getAccuracy()` The accuracy (minimum score) to be used, unless overridden in `suggestSimilar(String, int, IndexReader, String, SuggestMode, float)`, to decide whether a suggestion is included or not.
    `Comparator<SuggestWord>` | `getComparator()` Gets the comparator in use for ranking suggestions.
    `StringDistance` | `getStringDistance()` Returns the `StringDistance` instance used by this `SpellChecker` instance.
    `void` | `indexDictionary(Dictionary dict, IndexWriterConfig config, boolean fullMerge)` Indexes the data from the given `Dictionary`.
    `void` | `setAccuracy(float acc)` Sets the accuracy 0 < minScore < 1; default `DEFAULT_ACCURACY`
    `void` | `setComparator(Comparator<SuggestWord> comparator)` Sets the `Comparator` for the `SuggestWordQueue`.
    `void` | `setSpellIndex(Directory spellIndexDir)` Use a different index as the spell checker index or re-open the existing index if `spellIndex` is the same value as given in the constructor.
    `void` | `setStringDistance(StringDistance sd)` Sets the `StringDistance` implementation for this `SpellChecker` instance.
    `String[]` | `suggestSimilar(String word, int numSug)` Suggest similar words.
    `String[]` | `suggestSimilar(String word, int numSug, float accuracy)` Suggest similar words.
    `String[]` | `suggestSimilar(String word, int numSug, IndexReader ir, String field, SuggestMode suggestMode)` Calls `suggestSimilar(word, numSug, ir, suggestMode, field, this.accuracy)`
    `String[]` | `suggestSimilar(String word, int numSug, IndexReader ir, String field, SuggestMode suggestMode, float accuracy)` Suggest similar words (optionally restricted to a field of an index).

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### DEFAULT_ACCURACY

          public static final float DEFAULT_ACCURACY

      The default minimum score to use, if not specified by calling `setAccuracy(float)` .
      See Also:
        Constant Field Values

    - #### F_WORD

          public static final String F_WORD

      Field name for each word in the ngram index.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### SpellChecker

          public SpellChecker(Directory spellIndex,
                              StringDistance sd)
                       throws IOException

      Use the given directory as a spell checker index. The directory is created if it doesn't exist yet.
      Parameters:
        `spellIndex` - the spell index directory
        `sd` - the `StringDistance` measurement to use
      Throws:
        `IOException` - if Spellchecker can not open the directory

    - #### SpellChecker

          public SpellChecker(Directory spellIndex)
                       throws IOException

      Use the given directory as a spell checker index with a `LevenshteinDistance` as the default `StringDistance`. The directory is created if it doesn't exist yet.
      Parameters:
        `spellIndex` - the spell index directory
      Throws:
        `IOException` - if spellchecker can not open the directory

    - #### SpellChecker

          public SpellChecker(Directory spellIndex,
                              StringDistance sd,
                              Comparator<SuggestWord> comparator)
                       throws IOException

      Use the given directory as a spell checker index with the given `StringDistance` measure and the given `Comparator` for sorting the results.
      Parameters:
        `spellIndex` - The spelling index
        `sd` - The distance
        `comparator` - The comparator
      Throws:
        `IOException` - if there is a problem opening the index

  - ### Method Detail

    - #### setSpellIndex

          public void setSpellIndex(Directory spellIndexDir)
                             throws IOException

      Use a different index as the spell checker index or re-open the existing index if `spellIndex` is the same value as given in the constructor.
      Parameters:
        `spellIndexDir` - the spell directory to use
      Throws:
        `AlreadyClosedException` - if the Spellchecker is already closed
        `IOException` - if spellchecker can not open the directory

    - #### setComparator

          public void setComparator(Comparator<SuggestWord> comparator)

      Sets the `Comparator` for the `SuggestWordQueue`.
      Parameters:
        `comparator` - the comparator

    - #### getComparator

          public Comparator<SuggestWord> getComparator()

      Gets the comparator in use for ranking suggestions.
      See Also:
        `setComparator(Comparator)`

    - #### setStringDistance

          public void setStringDistance(StringDistance sd)

      Sets the `StringDistance` implementation for this `SpellChecker` instance.
      Parameters:
        `sd` - the `StringDistance` implementation for this `SpellChecker` instance

    - #### getStringDistance

          public StringDistance getStringDistance()

      Returns the `StringDistance` instance used by this `SpellChecker` instance.
      Returns:
        the `StringDistance` instance used by this `SpellChecker` instance.

    - #### setAccuracy

          public void setAccuracy(float acc)

      Sets the accuracy 0 < minScore < 1; default `DEFAULT_ACCURACY`
      Parameters:
        `acc` - The new accuracy

    - #### getAccuracy

          public float getAccuracy()

      The accuracy (minimum score) to be used, unless overridden in `suggestSimilar(String, int, IndexReader, String, SuggestMode, float)`, to decide whether a suggestion is included or not.
      Returns:
        The current accuracy setting

    - #### suggestSimilar

          public String[] suggestSimilar(String word,
                                         int numSug)
                                  throws IOException

      Suggest similar words.

      As the Lucene similarity that is used to fetch the most relevant n-grammed terms is not the same as the edit distance strategy used to calculate the best matching spell-checked word from the hits that Lucene found, one usually has to retrieve a couple of numSug's in order to get the true best match.

      I.e. if numSug == 1, don't count on that suggestion being the best one. Thus, you should set this value to at least 5 for a good suggestion.

      Parameters:
        `word` - the word you want a spell check done on
        `numSug` - the number of suggested words
      Returns:
        String[]
      Throws:
        `IOException` - if the underlying index throws an `IOException`
        `AlreadyClosedException` - if the Spellchecker is already closed
      See Also:
        `suggestSimilar(String, int, IndexReader, String, SuggestMode, float)`

    - #### suggestSimilar

          public String[] suggestSimilar(String word,
                                         int numSug,
                                         float accuracy)
                                  throws IOException

      Suggest similar words.

      As the Lucene similarity that is used to fetch the most relevant n-grammed terms is not the same as the edit distance strategy used to calculate the best matching spell-checked word from the hits that Lucene found, one usually has to retrieve a couple of numSug's in order to get the true best match.

      I.e. if numSug == 1, don't count on that suggestion being the best one. Thus, you should set this value to at least 5 for a good suggestion.

      Parameters:
        `word` - the word you want a spell check done on
        `numSug` - the number of suggested words
        `accuracy` - The minimum score a suggestion must have in order to qualify for inclusion in the results
      Returns:
        String[]
      Throws:
        `IOException` - if the underlying index throws an `IOException`
        `AlreadyClosedException` - if the Spellchecker is already closed
      See Also:
        `suggestSimilar(String, int, IndexReader, String, SuggestMode, float)`

    - #### suggestSimilar

          public String[] suggestSimilar(String word,
                                         int numSug,
                                         IndexReader ir,
                                         String field,
                                         SuggestMode suggestMode)
                                  throws IOException

      Calls `suggestSimilar(word, numSug, ir, suggestMode, field, this.accuracy)`
      Throws:
        `IOException`

    - #### suggestSimilar

          public String[] suggestSimilar(String word,
                                         int numSug,
                                         IndexReader ir,
                                         String field,
                                         SuggestMode suggestMode,
                                         float accuracy)
                                  throws IOException

      Suggest similar words (optionally restricted to a field of an index).

      As the Lucene similarity that is used to fetch the most relevant n-grammed terms is not the same as the edit distance strategy used to calculate the best matching spell-checked word from the hits that Lucene found, one usually has to retrieve a couple of numSug's in order to get the true best match.

      I.e. if numSug == 1, don't count on that suggestion being the best one. Thus, you should set this value to at least 5 for a good suggestion.

      Parameters:
        `word` - the word you want a spell check done on
        `numSug` - the number of suggested words
        `ir` - the indexReader of the user index (can be null see field param)
        `field` - the field of the user index: if field is not null, the suggested words are restricted to the words present in this field.
        `suggestMode` - (NOTE: if indexReader==null and/or field==null, then this is overridden with SuggestMode.SUGGEST_ALWAYS)
        `accuracy` - The minimum score a suggestion must have in order to qualify for inclusion in the results
      Returns:
        String[] the sorted list of the suggest words with these 2 criteria: first criteria: the edit distance, second criteria (only if restricted mode): the popularity of the suggest words in the field of the user index
      Throws:
        `IOException` - if the underlying index throws an `IOException`
        `AlreadyClosedException` - if the Spellchecker is already closed

    - #### clearIndex

          public void clearIndex()
                          throws IOException

      Removes all terms from the spell check index.
      Throws:
        `IOException` - If there is a low-level I/O error.
        `AlreadyClosedException` - if the Spellchecker is already closed

    - #### exist

          public boolean exist(String word)
                        throws IOException

      Check whether the word exists in the index.
      Parameters:
        `word` - word to check
      Returns:
        true if the word exists in the index
      Throws:
        `IOException` - If there is a low-level I/O error.
        `AlreadyClosedException` - if the Spellchecker is already closed

    - #### indexDictionary

          public final void indexDictionary(Dictionary dict,
                                            IndexWriterConfig config,
                                            boolean fullMerge)
                                     throws IOException

      Indexes the data from the given `Dictionary`.
      Parameters:
        `dict` - Dictionary to index
        `config` - `IndexWriterConfig` to use
        `fullMerge` - whether or not the spellcheck index should be fully merged
      Throws:
        `AlreadyClosedException` - if the Spellchecker is already closed
        `IOException` - If there is a low-level I/O error.

    - #### close

          public void close()
                     throws IOException

      Close the IndexSearcher used by this SpellChecker
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Throws:
        `IOException` - if the close operation causes an `IOException`
        `AlreadyClosedException` - if the `SpellChecker` is already closed

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