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Java > Open Source Codes > java_cup > symbol


1 package java_cup;
2
3 /** This abstract class serves as the base class for grammar symbols (i.e.,
4  * both terminals and non-terminals). Each symbol has a name string, and
5  * a string giving the type of object that the symbol will be represented by
6  * on the runtime parse stack. In addition, each symbol maintains a use count
7  * in order to detect symbols that are declared but never used, and an index
8  * number that indicates where it appears in parse tables (index numbers are
9  * unique within terminals or non terminals, but not across both).
10  *
11  * @see java_cup.terminal
12  * @see java_cup.non_terminal
13  * @version last updated: 7/3/96
14  * @author Frank Flannery
15  */

16 public abstract class symbol {
17    /*-----------------------------------------------------------*/
18    /*--- Constructor(s) ----------------------------------------*/
19    /*-----------------------------------------------------------*/
20
21    /** Full constructor.
22     * @param nm the name of the symbol.
23     * @param tp a string with the type name.
24     */

25    public symbol(String JavaDoc nm, String JavaDoc tp)
26      {
27        /* sanity check */
28        if (nm == null) nm = "";
29
30        /* apply default if no type given */
31        if (tp == null) tp = "Object";
32
33        _name = nm;
34        _stack_type = tp;
35      }
36
37   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
38
39    /** Constructor with default type.
40     * @param nm the name of the symbol.
41     */

42    public symbol(String JavaDoc nm)
43      {
44        this(nm, null);
45      }
46
47    /*-----------------------------------------------------------*/
48    /*--- (Access to) Instance Variables ------------------------*/
49    /*-----------------------------------------------------------*/
50
51    /** String for the human readable name of the symbol. */
52    protected String JavaDoc _name;
53  
54    /** String for the human readable name of the symbol. */
55    public String JavaDoc name() {return _name;}
56
57   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
58
59    /** String for the type of object used for the symbol on the parse stack. */
60    protected String JavaDoc _stack_type;
61
62    /** String for the type of object used for the symbol on the parse stack. */
63    public String JavaDoc stack_type() {return _stack_type;}
64
65   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
66
67    /** Count of how many times the symbol appears in productions. */
68    protected int _use_count = 0;
69
70    /** Count of how many times the symbol appears in productions. */
71    public int use_count() {return _use_count;}
72
73    /** Increment the use count. */
74    public void note_use() {_use_count++;}
75  
76   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
77  
78   /** Index of this symbol (terminal or non terminal) in the parse tables.
79    * Note: indexes are unique among terminals and unique among non terminals,
80    * however, a terminal may have the same index as a non-terminal, etc.
81    */

82    protected int _index;
83  
84   /** Index of this symbol (terminal or non terminal) in the parse tables.
85    * Note: indexes are unique among terminals and unique among non terminals,
86    * however, a terminal may have the same index as a non-terminal, etc.
87    */

88    public int index() {return _index;}
89
90   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
91
92   /** Indicate if this is a non-terminal. Here in the base class we
93    * don't know, so this is abstract.
94    */

95   public abstract boolean is_non_term();
96
97   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
98
99   /** Convert to a string. */
100   public String JavaDoc toString()
101     {
102       return name();
103     }
104
105   /*-----------------------------------------------------------*/
106
107 }
108
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