org.apache.velocity.runtime.parser

Interface CharStream

All Known Implementing Classes:

VelocityCharStream

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 and 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 Detail

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.

Returns:

read char

Throws:

IOException

getEndColumn

int getEndColumn()

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

Returns:

ending column number

getEndLine

int getEndLine()

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

Returns:

ending line number

getBeginColumn

int getBeginColumn()

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

Returns:

starting column number

getBeginLine

int getBeginLine()

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

Returns:

starting line number

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 implemetation's responsibility to do this right.

Parameters:

amount -

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.

Returns:

next token start char

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.

Returns:

token image

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();
   }
   

Parameters:

len - suffix len

Returns:

suffix

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.