Element


1   /*
2    * Element.java
3    *
4    * This library is free software; you can redistribute it and/or
5    * modify it under the terms of the GNU Lesser General Public License
6    * as published by the Free Software Foundation; either version 2.1
7    * of the License, or (at your option) any later version.
8    *
9    * This library is distributed in the hope that it will be useful,
10   * but WITHOUT ANY WARRANTY; without even the implied warranty of
11   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12   * Lesser General Public License for more details.
13   *
14   * You should have received a copy of the GNU Lesser General Public
15   * License along with this library; if not, write to the Free
16   * Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
17   * MA 02111-1307, USA.
18   *
19   * Copyright (c) 2003-2005 Per Cederberg. All rights reserved.
20   */
21  
22  package net.percederberg.grammatica.parser.re;
23  
24  import java.io.IOException  ;
25  import java.io.PrintStream  ;
26  import java.io.PrintWriter  ;
27  
28  import net.percederberg.grammatica.parser.LookAheadReader;
29  
30  /**
31   * A regular expression element. This is the common base class for all
32   * regular expression elements, i.e. the parts of the regular
33   * expression.
34   *
35   * @author   Per Cederberg, <per at percederberg dot net>
36   * @version  1.5
37   */
38  abstract class Element implements Cloneable   {
39  
40      /**
41       * Creates a copy of this element. The copy will be an instance
42       * of the same class matching the same strings. Copies of elements
43       * are necessary to allow elements to cache intermediate results
44       * while matching strings without interfering with other threads.
45       *
46       * @return a copy of this element
47       */
48      public abstract Object   clone();
49  
50      /**
51       * Returns the length of a matching string starting at the
52       * specified position. The number of matches to skip can also be
53       * specified, but numbers higher than zero (0) cause a failed
54       * match for any element that doesn't attempt to combine other
55       * elements.
56       *
57       * @param m              the matcher being used
58       * @param input          the input character stream to match
59       * @param start          the starting position
60       * @param skip           the number of matches to skip
61       *
62       * @return the length of the longest matching string, or
63       *         -1 if no match was found
64       *
65       * @throws IOException if an I/O error occurred
66       */
67      public abstract int match(Matcher m,
68                                LookAheadReader input,
69                                int start,
70                                int skip)
71          throws IOException  ;
72  
73      /**
74       * Prints this element to the specified output stream.
75       *
76       * @param output         the output stream to use
77       * @param indent         the current indentation
78       */
79      public final void printTo(PrintStream   output, String   indent) {
80          PrintWriter    writer = new PrintWriter  (output);
81  
82          printTo(writer, indent);
83          writer.flush();
84      }
85  
86      /**
87       * Prints this element to the specified output stream.
88       *
89       * @param output         the output stream to use
90       * @param indent         the current indentation
91       */
92      public abstract void printTo(PrintWriter   output, String   indent);
93  
94  }
95
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