org.apache.lucene.analysis

## Class LookaheadTokenFilter<T extends LookaheadTokenFilter.Position>

- java.lang.Object
- - org.apache.lucene.util.AttributeSource
  - - org.apache.lucene.analysis.TokenStream
    - - org.apache.lucene.analysis.TokenFilter
      - - org.apache.lucene.analysis.LookaheadTokenFilter<T>

All Implemented Interfaces:
  Closeable, AutoCloseable

Direct Known Subclasses:
  MockGraphTokenFilter, MockRandomLookaheadTokenFilter

    public abstract class LookaheadTokenFilter<T extends LookaheadTokenFilter.Position>
    extends TokenFilter

An abstract TokenFilter to make it easier to build graph token filters requiring some lookahead. This class handles the details of buffering up tokens, recording them by position, restoring them, providing access to them, etc.

### Nested Class Summary

Nested Classes
`protected static class` `LookaheadTokenFilter.Position` Holds all state for a single position; subclass this to record other state at each position.

### Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

`AttributeSource.AttributeFactory, AttributeSource.State`

### Field Summary

Fields
`protected boolean` `end`
`protected int` `inputPos`
`protected OffsetAttribute` `offsetAtt`
`protected int` `outputPos`
`protected PositionIncrementAttribute` `posIncAtt`
`protected RollingBuffer<T>` `positions`
`protected PositionLengthAttribute` `posLenAtt`

### Fields inherited from class org.apache.lucene.analysis.TokenFilter

`input`

### Constructor Summary

Constructors
`protected` `LookaheadTokenFilter(TokenStream input)`

### Method Summary

Methods
`protected void` `afterPosition()` This is called when all input tokens leaving a given position have been returned.
`protected void` `insertToken()` Call this only from within afterPosition, to insert a new token.
`protected abstract T` `newPosition()`
`protected boolean` `nextToken()` Call this when you are done looking ahead; it will set the next token to return.
`protected boolean` `peekToken()` Returns true if there is a new token.
`void` `reset()`

### Methods inherited from class org.apache.lucene.analysis.TokenFilter

`close, end`

### Methods inherited from class org.apache.lucene.analysis.TokenStream

`incrementToken`

### Methods inherited from class org.apache.lucene.util.AttributeSource

`addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState`

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

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

### Field Detail

#### posIncAtt

    protected final PositionIncrementAttribute posIncAtt

#### posLenAtt

    protected final PositionLengthAttribute posLenAtt

#### offsetAtt

    protected final OffsetAttribute offsetAtt

#### inputPos

    protected int inputPos

#### outputPos

    protected int outputPos

#### end

    protected boolean end

#### positions

    protected final RollingBuffer<T extends LookaheadTokenFilter.Position> positions

### Constructor Detail

#### LookaheadTokenFilter

    protected LookaheadTokenFilter(TokenStream input)

### Method Detail

#### insertToken

    protected void insertToken()
                        throws IOException

Call this only from within afterPosition, to insert a new token. After calling this you should set any necessary token you need.

Throws:
  `IOException`

#### afterPosition

    protected void afterPosition()
                          throws IOException

This is called when all input tokens leaving a given position have been returned. Override this and call createToken and then set whichever token's attributes you want, if you want to inject a token starting from this position.

Throws:
  `IOException`

#### newPosition

    protected abstract T newPosition()

#### peekToken

    protected boolean peekToken()
                         throws IOException

Returns true if there is a new token.

Throws:
  `IOException`

#### nextToken

    protected boolean nextToken()
                         throws IOException

Call this when you are done looking ahead; it will set the next token to return. Return the boolean back to the caller.

Throws:
  `IOException`

#### reset

    public void reset()
               throws IOException

Overrides:
  `reset` in class `TokenFilter`
Throws:
  `IOException`