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
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
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.
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 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();
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.