package java_cup;/** This abstract class serves as the base class for grammar symbols (i.e., * both terminals and non-terminals).  Each symbol has a name string, and * a string giving the type of object that the symbol will be represented by * on the runtime parse stack.  In addition, each symbol maintains a use count * in order to detect symbols that are declared but never used, and an index * number that indicates where it appears in parse tables (index numbers are * unique within terminals or non terminals, but not across both). * * @see     java_cup.terminal * @see     java_cup.non_terminal * @version last updated: 7/3/96 * @author  Frank Flannery */public abstract class symbol {   /*-----------------------------------------------------------*/   /*--- Constructor(s) ----------------------------------------*/   /*-----------------------------------------------------------*/   /** Full constructor.    * @param nm the name of the symbol.    * @param tp a string with the type name.    */   public symbol(String nm, String tp)     {       /* sanity check */       if (nm == null) nm = "";       /* apply default if no type given */       if (tp == null) tp = "Object";       _name = nm;       _stack_type = tp;     }  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/   /** Constructor with default type.     * @param nm the name of the symbol.    */   public symbol(String nm)     {       this(nm, null);     }   /*-----------------------------------------------------------*/   /*--- (Access to) Instance Variables ------------------------*/   /*-----------------------------------------------------------*/   /** String for the human readable name of the symbol. */   protected String _name;     /** String for the human readable name of the symbol. */   public String name() {return _name;}  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/   /** String for the type of object used for the symbol on the parse stack. */   protected String _stack_type;   /** String for the type of object used for the symbol on the parse stack. */   public String stack_type() {return _stack_type;}  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/   /** Count of how many times the symbol appears in productions. */   protected int _use_count = 0;   /** Count of how many times the symbol appears in productions. */   public int use_count() {return _use_count;}   /** Increment the use count. */    public void note_use() {_use_count++;}   /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/   /** Index of this symbol (terminal or non terminal) in the parse tables.   *  Note: indexes are unique among terminals and unique among non terminals,   *  however, a terminal may have the same index as a non-terminal, etc.    */   protected int _index;   /** Index of this symbol (terminal or non terminal) in the parse tables.   *  Note: indexes are unique among terminals and unique among non terminals,   *  however, a terminal may have the same index as a non-terminal, etc.    */   public int index() {return _index;}  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/  /** Indicate if this is a non-terminal.  Here in the base class we   *  don't know, so this is abstract.     */  public abstract boolean is_non_term();  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/  /** Convert to a string. */  public String toString()    {      return name();    }  /*-----------------------------------------------------------*/}