Package org.apache.lucene.queryparser.charstream

# Interface CharStream

All Known Implementing Classes:
  `FastCharStream`

public interface CharStream
This interface describes a character stream that maintains line and column number positions of the characters. It also has the capability to backup the stream to some extent. An implementation of this interface is used in the TokenManager implementation generated by JavaCCParser.

All the methods except backup can be implemented in any fashion. backup needs to be implemented correctly for the correct operation of the lexer. Rest of the methods are all used to get information like line number, column number and the String that constitutes a token and are not used by the lexer. Hence their implementation won't affect the generated lexer's operation.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `backup(int amount)`
  Backs up the input stream by amount steps.
  `char`
  `BeginToken()`
  Returns the next character that marks the beginning of the next token.
  `void`
  `Done()`
  The lexer calls this function to indicate that it is done with the stream and hence implementations can free any resources held by this class.
  `int`
  `getBeginColumn()`
  Returns the column number of the first character for current token (being matched after the last call to BeginTOken).
  `int`
  `getBeginLine()`
  Returns the line number of the first character for current token (being matched after the last call to BeginTOken).
  `int`
  `getEndColumn()`
  Returns the column number of the last character for current token (being matched after the last call to BeginTOken).
  `int`
  `getEndLine()`
  Returns the line number of the last character for current token (being matched after the last call to BeginTOken).
  `String`
  `GetImage()`
  Returns a string made up of characters from the marked token beginning to the current buffer position.
  `char[]`
  `GetSuffix(int len)`
  Returns an array of characters that make up the suffix of length 'len' for the currently matched token.
  `char`
  `readChar()`
  Returns the next character from the selected input.

- ## Method Details

  - ### readChar

    char readChar() throws IOException
    Returns the next character from the selected input. The method of selecting the input is the responsibility of the class implementing this interface. Can throw any java.io.IOException.
    Throws:
      `IOException`

  - ### getEndColumn

    int getEndColumn()
    Returns the column number of the last character for current token (being matched after the last call to BeginTOken).

  - ### getEndLine

    int getEndLine()
    Returns the line number of the last character for current token (being matched after the last call to BeginTOken).

  - ### getBeginColumn

    int getBeginColumn()
    Returns the column number of the first character for current token (being matched after the last call to BeginTOken).

  - ### getBeginLine

    int getBeginLine()
    Returns the line number of the first character for current token (being matched after the last call to BeginTOken).

  - ### backup

    void backup(int amount)
    Backs up the input stream by amount steps. Lexer calls this method if it had already read some characters, but could not use them to match a (longer) token. So, they will be used again as the prefix of the next token and it is the implementation's responsibility to do this right.

  - ### BeginToken

    char BeginToken() throws IOException
    Returns the next character that marks the beginning of the next token. All characters must remain in the buffer between two successive calls to this method to implement backup correctly.
    Throws:
      `IOException`

  - ### GetImage

    String GetImage()
    Returns a string made up of characters from the marked token beginning to the current buffer position. Implementations have the choice of returning anything that they want to. For example, for efficiency, one might decide to just return null, which is a valid implementation.

  - ### GetSuffix

    char[] GetSuffix(int len)
    Returns an array of characters that make up the suffix of length 'len' for the currently matched token. This is used to build up the matched string for use in actions in the case of MORE. A simple and inefficient implementation of this is as follows :

    { String t = GetImage(); return t.substring(t.length() - len, t.length()).toCharArray(); }

  - ### Done

    void Done()
    The lexer calls this function to indicate that it is done with the stream and hence implementations can free any resources held by this class. Again, the body of this function can be just empty and it will not affect the lexer's operation.