001    /* Generated By:JavaCC: Do not edit this line. CharStream.java Version 3.0 */
002    package org.w3c.flute.parser;
003    
004    /**
005     * This interface describes a character stream that maintains line and
006     * column number positions of the characters.  It also has the capability
007     * to backup the stream to some extent.  An implementation of this
008     * interface is used in the TokenManager implementation generated by
009     * JavaCCParser.
010     *
011     * All the methods except backup can be implemented in any fashion. backup
012     * needs to be implemented correctly for the correct operation of the lexer.
013     * Rest of the methods are all used to get information like line number,
014     * column number and the String that constitutes a token and are not used
015     * by the lexer. Hence their implementation won't affect the generated lexer's
016     * operation.
017     */
018    
019    public interface CharStream {
020    
021      /**
022       * Returns the next character from the selected input.  The method
023       * of selecting the input is the responsibility of the class
024       * implementing this interface.  Can throw any java.io.IOException.
025       */
026      char readChar() throws java.io.IOException;
027    
028      /**
029       * Returns the column position of the character last read.
030       * @deprecated 
031       * @see #getEndColumn
032       */
033      int getColumn();
034    
035      /**
036       * Returns the line number of the character last read.
037       * @deprecated 
038       * @see #getEndLine
039       */
040      int getLine();
041    
042      /**
043       * Returns the column number of the last character for current token (being
044       * matched after the last call to BeginTOken).
045       */
046      int getEndColumn();
047    
048      /**
049       * Returns the line number of the last character for current token (being
050       * matched after the last call to BeginTOken).
051       */
052      int getEndLine();
053    
054      /**
055       * Returns the column number of the first character for current token (being
056       * matched after the last call to BeginTOken).
057       */
058      int getBeginColumn();
059    
060      /**
061       * Returns the line number of the first character for current token (being
062       * matched after the last call to BeginTOken).
063       */
064      int getBeginLine();
065    
066      /**
067       * Backs up the input stream by amount steps. Lexer calls this method if it
068       * had already read some characters, but could not use them to match a
069       * (longer) token. So, they will be used again as the prefix of the next
070       * token and it is the implemetation's responsibility to do this right.
071       */
072      void backup(int amount);
073    
074      /**
075       * Returns the next character that marks the beginning of the next token.
076       * All characters must remain in the buffer between two successive calls
077       * to this method to implement backup correctly.
078       */
079      char BeginToken() throws java.io.IOException;
080    
081      /**
082       * Returns a string made up of characters from the marked token beginning 
083       * to the current buffer position. Implementations have the choice of returning
084       * anything that they want to. For example, for efficiency, one might decide
085       * to just return null, which is a valid implementation.
086       */
087      String GetImage();
088    
089      /**
090       * Returns an array of characters that make up the suffix of length 'len' for
091       * the currently matched token. This is used to build up the matched string
092       * for use in actions in the case of MORE. A simple and inefficient
093       * implementation of this is as follows :
094       *
095       *   {
096       *      String t = GetImage();
097       *      return t.substring(t.length() - len, t.length()).toCharArray();
098       *   }
099       */
100      char[] GetSuffix(int len);
101    
102      /**
103       * The lexer calls this function to indicate that it is done with the stream
104       * and hence implementations can free any resources held by this class.
105       * Again, the body of this function can be just empty and it will not
106       * affect the lexer's operation.
107       */
108      void Done();
109    
110    }