Package org.apache.lucene.util.fst

Class FST<T>

java.lang.Object

org.apache.lucene.util.fst.FST<T>

public final class FST<T>
extends Object

Represents an finite state machine (FST), using a compact byte[] format.

The format is similar to what's used by Morfologik (http://sourceforge.net/projects/morfologik).

See the package documentation for some simple examples.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	FST.Arc<T>	Represents a single arc.
static class	FST.BytesReader	Reads bytes stored in an FST.
static enum	FST.INPUT_TYPE	Specifies allowed range of each int input label for this FST.

Field Summary

Fields

Modifier and Type	Field	Description
long	arcCount
long	arcWithOutputCount
static final int	DEFAULT_MAX_BLOCK_BITS
static final int	END_LABEL	If arc has this label then that arc is final/accepted
final FST.INPUT_TYPE	inputType
long	nodeCount
final Outputs<T>	outputs

Constructor Summary

Constructors

Constructor	Description
FST(DataInput in, Outputs<T> outputs)	Load a previously saved FST.
FST(DataInput in, Outputs<T> outputs, int maxBlockBits)	Load a previously saved FST; maxBlockBits allows you to control the size of the byte[] pages used to hold the FST bytes.

Method Summary

Modifier and Type	Method	Description
FST.Arc<T>	findTargetArc(int labelToMatch, FST.Arc<T> follow, FST.Arc<T> arc, FST.BytesReader in)	Finds an arc leaving the incoming arc, replacing the arc in place.
long	getArcCount()
long	getArcWithOutputCount()
FST.BytesReader	getBytesReader()	Returns a FST.BytesReader for this FST, positioned at position 0.
T	getEmptyOutput()
FST.Arc<T>	getFirstArc(FST.Arc<T> arc)	Fills virtual 'start' arc, ie, an empty incoming arc to the FST's start node
FST.INPUT_TYPE	getInputType()
long	getNodeCount()
static <T> FST<T>	read(File file, Outputs<T> outputs)	Reads an automaton from a file.
FST.Arc<T>	readFirstRealTargetArc(long node, FST.Arc<T> arc, FST.BytesReader in)
FST.Arc<T>	readFirstTargetArc(FST.Arc<T> follow, FST.Arc<T> arc, FST.BytesReader in)	Follow the follow arc and read the first arc of its target; this changes the provided arc (2nd arg) in-place and returns it.
FST.Arc<T>	readLastTargetArc(FST.Arc<T> follow, FST.Arc<T> arc, FST.BytesReader in)	Follows the follow arc and reads the last arc of its target; this changes the provided arc (2nd arg) in-place and returns it.
FST.Arc<T>	readNextArc(FST.Arc<T> arc, FST.BytesReader in)	In-place read; returns the arc.
int	readNextArcLabel(FST.Arc<T> arc, FST.BytesReader in)	Peeks at next arc's label; does not alter arc.
FST.Arc<T>	readNextRealArc(FST.Arc<T> arc, FST.BytesReader in)	Never returns null, but you should never call this if arc.isLast() is true.
void	readRootArcs(FST.Arc<T>[] arcs)
void	save(File file)	Writes an automaton to a file.
void	save(DataOutput out)
long	sizeInBytes()	Returns bytes used to represent the FST
static <T> boolean	targetHasArcs(FST.Arc<T> arc)	returns true if the node at this address has any outgoing arcs

Methods inherited from class java.lang.Object

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

Field Details

inputType

public final FST.INPUT_TYPE inputType

outputs

public final Outputs<T> outputs

nodeCount

public long nodeCount

arcCount

public long arcCount

arcWithOutputCount

public long arcWithOutputCount

END_LABEL

public static final int END_LABEL

If arc has this label then that arc is final/accepted

See Also:

• Constant Field Values

DEFAULT_MAX_BLOCK_BITS

public static final int DEFAULT_MAX_BLOCK_BITS

Constructor Details

FST

public FST(DataInput in,
 Outputs<T> outputs)
    throws IOException

Load a previously saved FST.

Throws:

IOException

FST

public FST(DataInput in,
 Outputs<T> outputs,
 int maxBlockBits)
    throws IOException

Load a previously saved FST; maxBlockBits allows you to control the size of the byte[] pages used to hold the FST bytes.

Throws:

IOException

Method Details

getInputType

public FST.INPUT_TYPE getInputType()

sizeInBytes

public long sizeInBytes()

Returns bytes used to represent the FST

readRootArcs

public void readRootArcs(FST.Arc<T>[] arcs)
                  throws IOException

Throws:

IOException

getEmptyOutput

public T getEmptyOutput()

save

public void save(DataOutput out)
          throws IOException

Throws:

IOException

save

public void save(File file)
          throws IOException

Writes an automaton to a file.

Throws:

IOException

read

public static <T> FST<T> read(File file,
 Outputs<T> outputs)
                       throws IOException

Reads an automaton from a file.

Throws:

IOException

targetHasArcs

public static <T> boolean targetHasArcs(FST.Arc<T> arc)

returns true if the node at this address has any outgoing arcs

getFirstArc

public FST.Arc<T> getFirstArc(FST.Arc<T> arc)

Fills virtual 'start' arc, ie, an empty incoming arc to the FST's start node

readLastTargetArc

public FST.Arc<T> readLastTargetArc(FST.Arc<T> follow,
 FST.Arc<T> arc,
 FST.BytesReader in)
                             throws IOException

Follows the follow arc and reads the last arc of its target; this changes the provided arc (2nd arg) in-place and returns it.

Returns:

Returns the second argument (arc).

Throws:

IOException

readFirstTargetArc

public FST.Arc<T> readFirstTargetArc(FST.Arc<T> follow,
 FST.Arc<T> arc,
 FST.BytesReader in)
                              throws IOException

Follow the follow arc and read the first arc of its target; this changes the provided arc (2nd arg) in-place and returns it.

Returns:

Returns the second argument (arc).

Throws:

IOException

readFirstRealTargetArc

public FST.Arc<T> readFirstRealTargetArc(long node,
 FST.Arc<T> arc,
 FST.BytesReader in)
                                  throws IOException

Throws:

IOException

readNextArc

public FST.Arc<T> readNextArc(FST.Arc<T> arc,
 FST.BytesReader in)
                       throws IOException

In-place read; returns the arc.

Throws:

IOException

readNextArcLabel

public int readNextArcLabel(FST.Arc<T> arc,
 FST.BytesReader in)
                     throws IOException

Peeks at next arc's label; does not alter arc. Do not call this if arc.isLast()!

Throws:

IOException

readNextRealArc

public FST.Arc<T> readNextRealArc(FST.Arc<T> arc,
 FST.BytesReader in)
                           throws IOException

Never returns null, but you should never call this if arc.isLast() is true.

Throws:

IOException

findTargetArc

public FST.Arc<T> findTargetArc(int labelToMatch,
 FST.Arc<T> follow,
 FST.Arc<T> arc,
 FST.BytesReader in)
                         throws IOException

Finds an arc leaving the incoming arc, replacing the arc in place. This returns null if the arc was not found, else the incoming arc.

Throws:

IOException

getNodeCount

public long getNodeCount()

getArcCount

public long getArcCount()

getArcWithOutputCount

public long getArcWithOutputCount()

getBytesReader

public FST.BytesReader getBytesReader()

Returns a FST.BytesReader for this FST, positioned at position 0.