symbol_set


1   
2   package com.sun.java_cup.internal;
3   
4   import java.util.Hashtable  ;
5   import java.util.Enumeration  ;
6   
7   /** This class represents a set of symbols and provides a series of 
8    *  set operations to manipulate them.
9    *
10   * @see     com.sun.java_cup.internal.symbol
11   * @version last updated: 11/25/95
12   * @author  Scott Hudson
13   */
14  public class symbol_set {
15  
16    /*-----------------------------------------------------------*/
17    /*--- Constructor(s) ----------------------------------------*/
18    /*-----------------------------------------------------------*/
19  
20    /** Constructor for an empty set. */
21    public symbol_set() { }
22  
23    /** Constructor for cloning from another set. 
24     * @param other the set we are cloning from.
25     */
26    public symbol_set(symbol_set other) throws internal_error
27      {
28        not_null(other);
29        _all = (Hashtable  )other._all.clone();
30      }
31  
32    /*-----------------------------------------------------------*/
33    /*--- (Access to) Instance Variables ------------------------*/
34    /*-----------------------------------------------------------*/
35  
36    /** A hash table to hold the set. Symbols are keyed using their name string. 
37     */
38    protected Hashtable   _all = new Hashtable  (11);
39  
40    /** Access to all elements of the set. */
41    public Enumeration   all() {return _all.elements();}
42  
43    /** size of the set */
44    public int size() {return _all.size();}
45  
46    /*-----------------------------------------------------------*/
47    /*--- (Access to) Instance Variables ------------------------*/
48    /*-----------------------------------------------------------*/
49  
50    /** Helper function to test for a null object and throw an exception
51     *  if one is found.
52     * @param obj the object we are testing.
53     */
54    protected void not_null(Object   obj) throws internal_error
55      {
56        if (obj == null) 
57      throw new internal_error("Null object used in set operation");
58      }
59  
60    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
61  
62    /** Determine if the set contains a particular symbol. 
63     * @param sym the symbol we are looking for.
64     */
65    public boolean contains(symbol sym) {return _all.containsKey(sym.name());}
66  
67    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
68  
69    /** Determine if this set is an (improper) subset of another. 
70     * @param other the set we are testing against.
71     */
72    public boolean is_subset_of(symbol_set other) throws internal_error
73      {
74        not_null(other);
75  
76        /* walk down our set and make sure every element is in the other */
77        for (Enumeration   e = all(); e.hasMoreElements(); )
78      if (!other.contains((symbol)e.nextElement()))
79        return false;
80  
81        /* they were all there */
82        return true;
83      }
84  
85    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
86  
87    /** Determine if this set is an (improper) superset of another. 
88     * @param other the set we are are testing against.
89     */
90    public boolean is_superset_of(symbol_set other) throws internal_error
91      {
92        not_null(other);
93        return other.is_subset_of(this);
94      }
95  
96    /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
97  
98    /** Add a single symbol to the set.  
99     * @param sym the symbol we are adding.
100    * @return true if this changes the set.
101    */
102   public boolean add(symbol sym) throws internal_error
103     {
104       Object   previous;
105 
106       not_null(sym); 
107 
108       /* put the object in */
109       previous = _all.put(sym.name(),sym);
110 
111       /* if we had a previous, this is no change */
112       return previous == null;
113     }
114 
115   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
116 
117   /** Remove a single symbol if it is in the set. 
118    * @param sym the symbol we are removing.
119    */
120   public void remove(symbol sym) throws internal_error
121     {
122       not_null(sym); 
123       _all.remove(sym.name());
124     }
125 
126   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
127 
128   /** Add (union) in a complete set.  
129    * @param other the set we are adding in.
130    * @return true if this changes the set. 
131    */
132   public boolean add(symbol_set other) throws internal_error
133     {
134       boolean result = false;
135 
136       not_null(other);
137 
138       /* walk down the other set and do the adds individually */
139       for (Enumeration   e = other.all(); e.hasMoreElements(); )
140     result = add((symbol)e.nextElement()) || result;
141 
142       return result;
143     }
144 
145   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
146 
147   /** Remove (set subtract) a complete set. 
148    * @param other the set we are removing.
149    */
150   public void remove(symbol_set other) throws internal_error
151     {
152       not_null(other);
153 
154       /* walk down the other set and do the removes individually */
155       for (Enumeration   e = other.all(); e.hasMoreElements(); )
156     remove((symbol)e.nextElement());
157     }
158 
159   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
160 
161   /** Equality comparison. */
162   public boolean equals(symbol_set other) 
163     {
164       if (other == null || other.size() != size()) return false;
165 
166       /* once we know they are the same size, then improper subset does test */
167       try {
168         return is_subset_of(other);
169       } catch (internal_error e) {
170     /* can't throw the error (because super class doesn't), so we crash */
171     e.crash();
172     return false;
173       }
174     }
175 
176   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
177 
178   /** Generic equality comparison. */
179   public boolean equals(Object   other)
180     {
181       if (!(other instanceof symbol_set))
182     return false;
183       else
184     return equals((symbol_set)other);
185     }
186 
187   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
188 
189   /** Compute a hash code. */
190   public int hashCode()
191     {
192       int result = 0;
193       int cnt;
194       Enumeration   e;
195 
196       /* hash together codes from at most first 5 elements */
197       for (e = all(), cnt=0 ; e.hasMoreElements() && cnt<5; cnt++)
198     result ^= ((symbol)e.nextElement()).hashCode();
199 
200       return result;
201     }
202 
203   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
204 
205   /** Convert to a string. */
206   public String   toString()
207     {
208       String   result;
209       boolean comma_flag;
210 
211       result = "{";
212       comma_flag = false;
213       for (Enumeration   e = all(); e.hasMoreElements(); )
214     {
215       if (comma_flag)
216         result += ", ";
217       else
218         comma_flag = true;
219 
220       result += ((symbol)e.nextElement()).name();
221     }
222       result += "}";
223 
224       return result;
225     }
226 
227   /*-----------------------------------------------------------*/
228 
229 }
230 
231 
232
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