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
    Modifier and Type | Class and Description
    --- | ---
    `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.State`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `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`

    - ### Fields inherited from class org.apache.lucene.analysis.TokenStream

      `DEFAULT_TOKEN_ATTRIBUTE_FACTORY`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `LookaheadTokenFilter(TokenStream input)`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `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, endAttributes, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, removeAllAttributes, restoreState, toString`

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

      `clone, finalize, getClass, notify, notifyAll, 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 insertToken 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`

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