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
`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
`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