Package org.apache.lucene.search.suggest.fst

Class FSTCompletion

java.lang.Object

org.apache.lucene.search.suggest.fst.FSTCompletion

public class FSTCompletion
extends Object

Finite state automata based implementation of "autocomplete" functionality.

See Also:

FSTCompletionBuilder

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FSTCompletion.Completion	A single completion for a given key.

Field Summary

Fields

Modifier and Type	Field	Description
static int	DEFAULT_BUCKETS	Default number of buckets.

Constructor Summary

Constructors

Constructor	Description
FSTCompletion(FST<Object> automaton)	Defaults to higher weights first and exact first.
FSTCompletion(FST<Object> automaton, boolean higherWeightsFirst, boolean exactFirst)	Constructs an FSTCompletion, specifying higherWeightsFirst and exactFirst.

Method Summary

Modifier and Type	Method	Description
int	getBucket(CharSequence key)	Returns the bucket assigned to a given key (if found) or -1 if no exact match exists.
int	getBucketCount()	Returns the bucket count (discretization thresholds).
FST<Object>	getFST()	Returns the internal automaton.
Stream<FSTCompletion.Completion>	lookup(CharSequence key)	Lookup suggestions to key and return a stream of matching completions.
List<FSTCompletion.Completion>	lookup(CharSequence key, int num)	Lookup suggestions to key.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_BUCKETS

public static final int DEFAULT_BUCKETS

Default number of buckets.

See Also:

Constant Field Values

Constructor Detail

FSTCompletion

public FSTCompletion(FST<Object> automaton,
                     boolean higherWeightsFirst,
                     boolean exactFirst)

Constructs an FSTCompletion, specifying higherWeightsFirst and exactFirst.

Parameters:

automaton - Automaton with completions. See FSTCompletionBuilder.

higherWeightsFirst - Return most popular suggestions first. This is the default behavior for this implementation. Setting it to false has no effect (use constant term weights to sort alphabetically only).

exactFirst - Find and push an exact match to the first position of the result list if found.

FSTCompletion

public FSTCompletion(FST<Object> automaton)

Defaults to higher weights first and exact first.

See Also:

FSTCompletion(FST, boolean, boolean)

Method Detail

lookup

public List<FSTCompletion.Completion> lookup(CharSequence key,
                                             int num)

Lookup suggestions to key.

Parameters:

key - The prefix to which suggestions should be sought.

num - At most this number of suggestions will be returned.

Returns:

Returns the suggestions, sorted by their approximated weight first (decreasing) and then alphabetically (UTF-8 codepoint order).

lookup

public Stream<FSTCompletion.Completion> lookup(CharSequence key)

Lookup suggestions to key and return a stream of matching completions. The stream fetches completions dynamically - it can be filtered and limited to acquire the desired number of completions without collecting all of them.

Parameters:

key - The prefix to which suggestions should be sought.

Returns:

Returns the suggestions

getBucketCount

public int getBucketCount()

Returns the bucket count (discretization thresholds).

getBucket

public int getBucket(CharSequence key)

Returns the bucket assigned to a given key (if found) or -1 if no exact match exists.

getFST

public FST<Object> getFST()

Returns the internal automaton.