Item


1   /*
2    *  Copyright (C) Chaperon. All rights reserved.
3    *  -------------------------------------------------------------------------
4    *  This software is published under the terms of the Apache Software License
5    *  version 1.1, a copy of which has been included  with this distribution in
6    *  the LICENSE file.
7    */
8   
9   package net.sourceforge.chaperon.process.extended;
10  
11  import net.sourceforge.chaperon.model.extended.Element;
12  import net.sourceforge.chaperon.model.extended.Pattern;
13  
14  /**
15   * Representation of a kernel state. q1 :=  q2 q2     q1=previous q2=pattern Possible positions: q1
16   * := .q2  q2    Shift q2 q1 :=  q2 .q2    Goto q2 / Reduce q2(0) if q2 is final state q1 :=  q2
17   * q2.   Reduce q1(2)
18   *
19   * @author <a HREF="mailto:stephan@apache.org">Stephan Michels</a>
20   * @version CVS $Id: Item.java,v 1.1 2004/01/04 16:49:12 benedikta Exp $
21   */
22  public class Item
23  {
24    public Item next = null;
25  
26    // reduce to the symbol, or previous pattern
27    public String   symbol;
28    public Pattern previous;
29  
30    // definition of the item
31    public Pattern pattern;
32  
33    // possible positions: 0,1,2
34    public int position;
35    public static final int SHIFT = 0;
36    public static final int GOTO = 1;
37    public static final int REDUCE = 2;
38  
39    // lookahead pattern of the item
40    public Pattern lookahead;
41    public boolean end = false;
42  
43    public Item(String   symbol, Pattern pattern, int position, Pattern lookahead)
44    {
45      if (symbol==null)
46        throw new IllegalArgumentException  ("Symbol is null");
47  
48      if (pattern==null)
49        throw new IllegalArgumentException  ("Pattern is null");
50  
51      if ((position<0) && (position>2))
52        throw new IllegalArgumentException  ("Only item positions 0,1 and 2 are allowed");
53  
54      if (lookahead instanceof Element)
55        throw new IllegalStateException  ("bla");
56  
57      this.symbol = symbol;
58      this.previous = null;
59      this.pattern = pattern;
60      this.position = position;
61  
62      //this.end = end;
63      this.lookahead = lookahead;
64    }
65  
66    public Item(Pattern previous, Pattern pattern, int position, Pattern lookahead)
67    {
68      if (previous==null)
69        throw new IllegalArgumentException  ("Previous pattern is null");
70  
71      if (pattern==null)
72        throw new IllegalArgumentException  ("Pattern is null");
73  
74      if ((position<0) && (position>2))
75        throw new IllegalArgumentException  ("Only item positions 0,1 and 2 are allowed");
76  
77      if (lookahead instanceof Element)
78        throw new IllegalStateException  ("bla");
79  
80      this.symbol = null;
81      this.previous = previous;
82      this.pattern = pattern;
83      this.position = position;
84  
85      //this.end = end;
86      this.lookahead = lookahead;
87    }
88  
89    public Item getFollowItem()
90    {
91      if (position<REDUCE)
92      {
93        if (symbol!=null)
94          return new Item(symbol, pattern, position+1, lookahead);
95  
96        return new Item(previous, pattern, position+1, lookahead);
97      }
98      else
99        return null;
100   }
101 
102   public boolean equals(Object   o)
103   {
104     if (o instanceof Item)
105     {
106       Item item = (Item)o;
107 
108       if (symbol!=null)
109         return (item.symbol!=null) && symbol.equals(item.symbol) && (pattern==item.pattern) &&
110                (position==item.position) && (lookahead==item.lookahead);
111 
112       return (previous==item.previous) && (pattern==item.pattern) && (position==item.position) &&
113              (lookahead==item.lookahead);
114     }
115 
116     return false;
117   }
118 
119   public String   toString()
120   {
121     StringBuffer   buffer = new StringBuffer  ();
122 
123     if (symbol!=null)
124       buffer.append(symbol);
125     else
126       buffer.append(previous);
127 
128     buffer.append(" := ");
129 
130     if (position==SHIFT)
131       buffer.append(".");
132 
133     buffer.append(pattern);
134     buffer.append(" ");
135 
136     if (position==GOTO)
137       buffer.append(".");
138 
139     buffer.append(pattern);
140 
141     if (position==REDUCE)
142       buffer.append(".");
143 
144     buffer.append(",");
145     buffer.append(lookahead);
146 
147     return buffer.toString();
148   }
149 }
150
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