terminal_set


1   
2   package com.sun.java_cup.internal;
3   
4   import java.util.BitSet  ;
5   
6   /** A set of terminals implemented as a bitset. 
7    * @version last updated: 11/25/95
8    * @author  Scott Hudson
9    */
10  public class terminal_set {
11  
12    /*-----------------------------------------------------------*/
13    /*--- Constructor(s) ----------------------------------------*/
14    /*-----------------------------------------------------------*/
15  
16    /** Constructor for an empty set. */
17    public terminal_set() 
18      { 
19        /* allocate the bitset at what is probably the right size */
20        _elements = new BitSet  (terminal.number());
21      }
22  
23    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
24  
25    /** Constructor for cloning from another set. 
26     * @param other the set we are cloning from.
27     */
28    public terminal_set(terminal_set other) 
29      throws internal_error
30      {
31        not_null(other);
32        _elements = (BitSet  )other._elements.clone();
33      }
34  
35    /*-----------------------------------------------------------*/
36    /*--- (Access to) Static (Class) Variables ------------------*/
37    /*-----------------------------------------------------------*/
38  
39    /** Constant for the empty set. */
40    public static final terminal_set EMPTY = new terminal_set();
41  
42    /*-----------------------------------------------------------*/
43    /*--- (Access to) Instance Variables ------------------------*/
44    /*-----------------------------------------------------------*/
45  
46    /** Bitset to implement the actual set. */
47    protected BitSet   _elements;
48  
49    /*-----------------------------------------------------------*/
50    /*--- General Methods ----------------------------------------*/
51    /*-----------------------------------------------------------*/
52  
53    /** Helper function to test for a null object and throw an exception if
54     *  one is found. 
55     * @param obj the object we are testing.
56     */
57    protected void not_null(Object   obj) throws internal_error
58      {
59        if (obj == null) 
60      throw new internal_error("Null object used in set operation");
61      }
62  
63    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
64  
65    /** Determine if the set is empty. */
66    public boolean empty()
67      {
68        return equals(EMPTY);
69      }
70  
71    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
72  
73    /** Determine if the set contains a particular terminal. 
74     * @param sym the terminal symbol we are looking for.
75     */
76    public boolean contains(terminal sym) 
77      throws internal_error
78      {
79        not_null(sym); 
80        return _elements.get(sym.index());
81      }
82  
83    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
84  
85    /** Given its index determine if the set contains a particular terminal. 
86     * @param indx the index of the terminal in question.
87     */
88    public boolean contains(int indx) 
89      {
90        return _elements.get(indx);
91      }
92  
93    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
94  
95    /** Determine if this set is an (improper) subset of another.
96     * @param other the set we are testing against.
97     */
98    public boolean is_subset_of(terminal_set other)
99      throws internal_error
100     {
101       not_null(other);
102 
103       /* make a copy of the other set */
104       BitSet   copy_other = (BitSet  )other._elements.clone();
105 
106       /* and or in */
107       copy_other.or(_elements);
108 
109       /* if it hasn't changed, we were a subset */
110       return copy_other.equals(other._elements);
111     }
112 
113   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
114 
115   /** Determine if this set is an (improper) superset of another.
116    * @param other the set we are testing against.
117    */
118   public boolean is_superset_of(terminal_set other)
119     throws internal_error
120     {
121       not_null(other);
122       return other.is_subset_of(this);
123     }
124 
125   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
126 
127   /** Add a single terminal to the set.  
128    * @param sym the terminal being added.
129    * @return true if this changes the set.
130    */
131   public boolean add(terminal sym) 
132     throws internal_error
133     {
134       boolean result;
135 
136       not_null(sym); 
137 
138       /* see if we already have this */ 
139       result = _elements.get(sym.index());
140 
141       /* if not we add it */
142       if (!result)
143     _elements.set(sym.index());
144 
145       return result;
146     }
147 
148   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
149 
150   /** Remove a terminal if it is in the set.
151    * @param sym the terminal being removed.
152    */
153   public void remove(terminal sym) 
154     throws internal_error
155     {
156       not_null(sym); 
157       _elements.clear(sym.index());
158     }
159 
160   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
161 
162   /** Add (union) in a complete set.  
163    * @param other the set being added.
164    * @return true if this changes the set.
165    */
166   public boolean add(terminal_set other)
167     throws internal_error
168     {
169       not_null(other);
170 
171       /* make a copy */
172       BitSet   copy = (BitSet  )_elements.clone();
173 
174       /* or in the other set */
175       _elements.or(other._elements);
176 
177       /* changed if we are not the same as the copy */
178       return !_elements.equals(copy);
179     }
180 
181   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
182 
183   /** Determine if this set intersects another.
184    * @param other the other set in question.
185    */
186    public boolean intersects(terminal_set other)
187      throws internal_error
188      {
189        not_null(other);
190 
191        /* make a copy of the other set */
192        BitSet   copy = (BitSet  )other._elements.clone();
193 
194        /* xor out our values */
195        copy.xor(this._elements);
196 
197        /* see if its different */
198        return !copy.equals(other._elements);
199      }
200 
201   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
202 
203   /** Equality comparison. */
204   public boolean equals(terminal_set other)
205     {
206       if (other == null) 
207     return false;
208       else
209     return _elements.equals(other._elements);
210     }
211 
212   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
213 
214   /** Generic equality comparison. */
215   public boolean equals(Object   other)
216     {
217       if (!(other instanceof terminal_set))
218     return false;
219       else
220     return equals((terminal_set)other);
221     }
222 
223   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
224 
225   /** Convert to string. */
226   public String   toString()
227     {
228       String   result;
229       boolean comma_flag;
230       
231       result = "{";
232       comma_flag = false;
233       for (int t = 0; t < terminal.number(); t++)
234     {
235       if (_elements.get(t))
236         {
237           if (comma_flag)
238             result += ", ";
239           else
240             comma_flag = true;
241 
242           result += terminal.find(t).name();
243         }
244     }
245       result += "}";
246 
247       return result;
248     }
249 
250   /*-----------------------------------------------------------*/
251 
252 }
253 
254
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