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Java > Open Source Codes > gnu > regexp > CharIndexed


1 /*
2  * gnu/regexp/CharIndexed.java
3  * Copyright (C) 1998-2001 Wes Biggs
4  *
5  * This library is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU Lesser General Public License as published
7  * by the Free Software Foundation; either version 2.1 of the License, or
8  * (at your option) any later version.
9  *
10  * This library is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13  * GNU Lesser General Public License for more details.
14  *
15  * You should have received a copy of the GNU Lesser General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
18  */
19 package gnu.regexp;
20
21 /**
22  * Defines the interface used internally so that different types of source
23  * text can be accessed in the same way. Built-in concrete classes provide
24  * support for String, StringBuffer, InputStream and char[] types.
25  * A class that is CharIndexed supports the notion of a cursor within a
26  * block of text. The cursor must be able to be advanced via the move()
27  * method. The charAt() method returns the character at the cursor position
28  * plus a given offset.
29  *
30  * @author <A HREF="mailto:wes@cacas.org">Wes Biggs</A>
31  */
32 public interface CharIndexed {
33     /**
34      * Defines a constant (0xFFFF was somewhat arbitrarily chosen)
35      * that can be returned by the charAt() function indicating that
36      * the specified index is out of range.
37      */
38     char OUT_OF_BOUNDS = '\uFFFF';
39
40     /**
41      * Returns the character at the given offset past the current cursor
42      * position in the input. The index of the current position is zero.
43      * It is possible for this method to be called with a negative index.
44      * This happens when using the '^' operator in multiline matching mode
45      * or the '\b' or '\<' word boundary operators. In any case, the lower
46      * bound is currently fixed at -2 (for '^' with a two-character newline).
47      *
48      * @param index the offset position in the character field to examine
49      * @return the character at the specified index, or the OUT_OF_BOUNDS
50      * character defined by this interface.
51      */
52     char charAt(int index);
53
54     /**
55      * Shifts the input buffer by a given number of positions. Returns
56      * true if the new cursor position is valid.
57      */
58     boolean move(int index);
59
60     /**
61      * Returns true if the most recent move() operation placed the cursor
62      * position at a valid position in the input.
63      */
64     boolean isValid();
65 }
66
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