java.lang.Object
- org.apache.lucene.util.fst.FST<T>

All Implemented Interfaces:

Accountable
```
public final class FST<T>
extends Object
implements Accountable
```
Represents an finite state machine (FST), using a compact byte[] format.
The format is similar to what's used by Morfologik (https://github.com/morfologik/morfologik-stemming).
See the package documentation for some simple examples.

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`	`FST.Arc<T>`	Represents a single arc.
`static class`	`FST.BytesReader`	Reads bytes stored in an FST.
`static class`	`FST.FSTMetadata<T>`	Represents the FST metadata.
`static class`	`FST.INPUT_TYPE`	Specifies allowed range of each int input label for this FST.

Field Summary

Fields
Modifier and Type	Field	Description
`static byte`	`ARCS_FOR_BINARY_SEARCH`	Value of the arc flags to declare a node with fixed length (sparse) arcs designed for binary search.
`static int`	`BIT_ARC_HAS_OUTPUT`	This flag is set if the arc has an output.
`static int`	`END_LABEL`	If arc has this label then that arc is final/accepted
`Outputs<T>`	`outputs`
`static int`	`VERSION_90`	Version that was used when releasing Lucene 9.0.
`static int`	`VERSION_CONTINUOUS_ARCS`	Version that started storing continuous arcs.
`static int`	`VERSION_CURRENT`	Current version.
`static int`	`VERSION_START`	First supported version, this is the version that was used when releasing Lucene 7.0.

Fields inherited from interface org.apache.lucene.util.Accountable
NULL_ACCOUNTABLE

Constructor Summary

Constructors
Constructor	Description
`FST(FST.FSTMetadata<T> metadata, DataInput in)`	Load a previously saved FST with a DataInput for metdata using an `OnHeapFSTStore` with maxBlockBits set to `DEFAULT_MAX_BLOCK_BITS`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
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.
`static <T> FST<T>`	`fromFSTReader(FST.FSTMetadata<T> fstMetadata, FSTReader fstReader)`	Create a FST from a `FSTReader`.
`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.FSTMetadata<T>`	`getMetadata()`
`long`	`numBytes()`
`long`	`ramBytesUsed()`	Return the memory usage of this object in bytes.
`static <T> FST<T>`	`read(Path path, Outputs<T> outputs)`	Reads an automaton from a file.
`FST.Arc<T>`	`readArcByContinuous(FST.Arc<T> arc, FST.BytesReader in, int rangeIndex)`	Reads a Continuous node arc, with the provided index in the label range.
`FST.Arc<T>`	`readArcByDirectAddressing(FST.Arc<T> arc, FST.BytesReader in, int rangeIndex)`	Reads a present direct addressing node arc, with the provided index in the label range.
`FST.Arc<T>`	`readArcByIndex(FST.Arc<T> arc, FST.BytesReader in, int idx)`
`FST.Arc<T>`	`readFirstRealTargetArc(long nodeAddress, 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.
`int`	`readLabel(DataInput in)`	Reads one BYTE1/2/4 label from the provided `DataInput`.
`FST.Arc<T>`	`readLastArcByContinuous(FST.Arc<T> arc, FST.BytesReader in)`	Reads the last arc of a continuous node.
`FST.Arc<T>`	`readLastArcByDirectAddressing(FST.Arc<T> arc, FST.BytesReader in)`	Reads the last arc of a direct addressing node.
`static <T> FST.FSTMetadata<T>`	`readMetadata(DataInput metaIn, Outputs<T> outputs)`	Read the FST metadata from DataInput
`FST.Arc<T>`	`readNextArc(FST.Arc<T> arc, FST.BytesReader in)`	In-place read; returns the 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`	`save(Path path)`	Writes an automaton to a file.
`void`	`save(DataOutput metaOut, DataOutput out)`	Save the FST to DataOutput.
`static <T> boolean`	`targetHasArcs(FST.Arc<T> arc)`	returns true if the node at this address has any outgoing arcs
`String`	`toString()`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.lucene.util.Accountable
getChildResources

Field Detail
- BIT_ARC_HAS_OUTPUT
```
public static final int BIT_ARC_HAS_OUTPUT
```
  This flag is set if the arc has an output.
  
  See Also:
  
  Constant Field Values
- ARCS_FOR_BINARY_SEARCH
```
public static final byte ARCS_FOR_BINARY_SEARCH
```
  Value of the arc flags to declare a node with fixed length (sparse) arcs designed for binary search.
  
  See Also:
  
  Constant Field Values
- VERSION_START
```
public static final int VERSION_START
```
  First supported version, this is the version that was used when releasing Lucene 7.0.
  
  See Also:
  
  Constant Field Values
- VERSION_CONTINUOUS_ARCS
```
public static final int VERSION_CONTINUOUS_ARCS
```
  Version that started storing continuous arcs.
  
  See Also:
  
  Constant Field Values
- VERSION_CURRENT
```
public static final int VERSION_CURRENT
```
  Current version.
  
  See Also:
  
  Constant Field Values
- VERSION_90
```
public static final int VERSION_90
```
  Version that was used when releasing Lucene 9.0.
  
  See Also:
  
  Constant Field Values
- END_LABEL
```
public static final int END_LABEL
```
  If arc has this label then that arc is final/accepted
  
  See Also:
  
  Constant Field Values
- outputs
```
public final Outputs<T> outputs
```

Constructor Detail
- FST
```
public FST(FST.FSTMetadata<T> metadata,
           DataInput in)
    throws IOException
```
  Load a previously saved FST with a DataInput for metdata using an OnHeapFSTStore with maxBlockBits set to DEFAULT_MAX_BLOCK_BITS
  
  Throws:
  
  IOException

Method Detail

fromFSTReader

public static <T> FST<T> fromFSTReader(FST.FSTMetadata<T> fstMetadata,
                                       FSTReader fstReader)

Create a FST from a FSTReader. Return null if the metadata is null.

Parameters:: fstMetadata - the metadata; fstReader - the FSTReader
Returns:: the FST

readMetadata

public static <T> FST.FSTMetadata<T> readMetadata(DataInput metaIn,
                                                  Outputs<T> outputs)
                                           throws IOException

Read the FST metadata from DataInput

Type Parameters:: T - the output type
Parameters:: metaIn - the DataInput of the metadata; outputs - the FST outputs
Returns:: the FST metadata
Throws:: IOException - if exception occurred during parsing

ramBytesUsed
```
public long ramBytesUsed()
```
Description copied from interface: Accountable

Return the memory usage of this object in bytes. Negative values are illegal.

Specified by:

ramBytesUsed in interface Accountable

toString
```
public String toString()
```
Overrides:

toString in class Object

numBytes
```
public long numBytes()
```

getEmptyOutput
```
public T getEmptyOutput()
```

getMetadata

public FST.FSTMetadata<T> getMetadata()

save
```
public void save(DataOutput metaOut,
                 DataOutput out)
          throws IOException
```
Save the FST to DataOutput.

Parameters:

metaOut - the DataOutput to write the metadata to

out - the DataOutput to write the FST bytes to

Throws:

IOException

save

public void save(Path path)
          throws IOException

Writes an automaton to a file.

Throws:: IOException

read

public static <T> FST<T> read(Path path,
                              Outputs<T> outputs)
                       throws IOException

Reads an automaton from a file.

Throws:: IOException

readLabel
```
public int readLabel(DataInput in)
              throws IOException
```
Reads one BYTE1/2/4 label from the provided DataInput.

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

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 nodeAddress,
                                         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

readArcByIndex

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

Throws:: IOException

readArcByContinuous

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

Reads a Continuous node arc, with the provided index in the label range.

Parameters:: rangeIndex - The index of the arc in the label range. It must be within the label range.
Throws:: IOException

readArcByDirectAddressing
```
public FST.Arc<T> readArcByDirectAddressing(FST.Arc<T> arc,
                                            FST.BytesReader in,
                                            int rangeIndex)
                                     throws IOException
```
Reads a present direct addressing node arc, with the provided index in the label range.

Parameters:

rangeIndex - The index of the arc in the label range. It must be present. The real arc offset is computed based on the presence bits of the direct addressing node.

Throws:

IOException

readLastArcByDirectAddressing

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

Reads the last arc of a direct addressing node. This method is equivalent to call readArcByDirectAddressing(Arc, BytesReader, int) with rangeIndex equal to


 arc.numArcs() - 1

, but it is faster.

Throws:: IOException

readLastArcByContinuous

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

Reads the last arc of a continuous node.

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

getBytesReader
```
public FST.BytesReader getBytesReader()
```
Returns a FST.BytesReader for this FST, positioned at position 0.

Class FST<T>

Nested Class Summary

Field Summary

Fields inherited from interface org.apache.lucene.util.Accountable

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface org.apache.lucene.util.Accountable

Field Detail

BIT_ARC_HAS_OUTPUT

ARCS_FOR_BINARY_SEARCH

VERSION_START

VERSION_CONTINUOUS_ARCS

VERSION_CURRENT

VERSION_90

END_LABEL

outputs

Constructor Detail

FST

Method Detail

fromFSTReader

readMetadata

ramBytesUsed

toString

numBytes

getEmptyOutput

getMetadata

save

save

read

readLabel

targetHasArcs

getFirstArc

readFirstTargetArc

readFirstRealTargetArc

readNextArc

readArcByIndex

readArcByContinuous

readArcByDirectAddressing

readLastArcByDirectAddressing

readLastArcByContinuous

readNextRealArc

findTargetArc

getBytesReader