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Java > Open Source Codes > gnu > regexp > CharIndexedReader


1 /*
2  * gnu/regexp/CharIndexedReader.java
3  * Copyright (C) 2001 Lee Sau Dan
4  * Based on gnu.regexp.CharIndexedInputStream by Wes Biggs
5  *
6  * This library is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU Lesser General Public License as published
8  * by the Free Software Foundation; either version 2.1 of the License, or
9  * (at your option) any later version.
10  *
11  * This library is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14  * GNU Lesser General Public License for more details.
15  *
16  * You should have received a copy of the GNU Lesser General Public License
17  * along with this program; if not, write to the Free Software
18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19  */
20
21 package gnu.regexp;
22 import java.io.Reader JavaDoc;
23 import java.io.BufferedReader JavaDoc;
24 import java.io.IOException JavaDoc;
25
26 // TODO: move(x) shouldn't rely on calling next() x times
27
28 class CharIndexedReader implements CharIndexed {
29     private static final int BUFFER_INCREMENT = 1024;
30     private static final int UNKNOWN = Integer.MAX_VALUE; // value for end
31
32     private final BufferedReader JavaDoc br;
33     // so that we don't try to reset() right away
34 private int index = -1;
35
36     private int bufsize = BUFFER_INCREMENT;
37
38     private int end = UNKNOWN;
39
40     private char cached = OUT_OF_BOUNDS;
41
42     // Big enough for a \r\n pair
43 // lookBehind[0] = most recent
44 // lookBehind[1] = second most recent
45 private char[] lookBehind = new char[] { OUT_OF_BOUNDS, OUT_OF_BOUNDS };
46   
47     CharIndexedReader(Reader JavaDoc reader, int index) {
48     if (reader instanceof BufferedReader JavaDoc) {
49         br = (BufferedReader JavaDoc) reader;
50     } else {
51         br = new BufferedReader JavaDoc(reader,BUFFER_INCREMENT);
52     }
53     next();
54     if (index > 0) move(index);
55     }
56     
57     private boolean next() {
58     lookBehind[1] = lookBehind[0];
59     lookBehind[0] = cached;
60
61     if (end == 1) {
62         cached = OUT_OF_BOUNDS;
63         return false;
64     }
65     end--; // closer to end
66
67     try {
68         if (index != -1) {
69         br.reset();
70         }
71         int i = br.read();
72         br.mark(bufsize);
73         if (i == -1) {
74         end = 1;
75         cached = OUT_OF_BOUNDS;
76         return false;
77         }
78
79         // convert the byte read into a char
80 cached = (char) i;
81         index = 1;
82     } catch (IOException JavaDoc e) {
83         e.printStackTrace();
84         cached = OUT_OF_BOUNDS;
85         return false;
86     }
87     return true;
88     }
89     
90     public char charAt(int index) {
91     if (index == 0) {
92         return cached;
93     } else if (index >= end) {
94         return OUT_OF_BOUNDS;
95     } else if (index >= bufsize) {
96         // Allocate more space in the buffer.
97 try {
98         while (bufsize <= index) bufsize += BUFFER_INCREMENT;
99         br.reset();
100         br.mark(bufsize);
101         br.skip(index-1);
102         } catch (IOException JavaDoc e) { }
103     } else if (this.index != index) {
104         try {
105         br.reset();
106         br.skip(index-1);
107         } catch (IOException JavaDoc e) { }
108     } else if (index == -1) {
109         return lookBehind[0];
110     } else if (index == -2) {
111         return lookBehind[1];
112     } else if (index < -2) {
113         return OUT_OF_BOUNDS;
114     }
115
116     char ch = OUT_OF_BOUNDS;
117     
118     try {
119         int i = br.read();
120         this.index = index+1; // this.index is index of next pos relative to charAt(0)
121 if (i == -1) {
122         // set flag that next should fail next time?
123 end = index;
124         return ch;
125         }
126         ch = (char) i;
127     } catch (IOException JavaDoc ie) { }
128     
129     return ch;
130     }
131     
132     public boolean move(int index) {
133     // move read position [index] clicks from 'charAt(0)'
134 boolean retval = true;
135     while (retval && (index-- > 0)) retval = next();
136     return retval;
137     }
138     
139     public boolean isValid() {
140     return (cached != OUT_OF_BOUNDS);
141     }
142 }
143
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