symtab.java

java语法解释器生成器

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright (C) 2001       Gerwin Klein <[e-mail]>                    *
 * Copyright (C) 2001       Bernhard Rumpe <[e-mail]>               *
 * All rights reserved.                                                    *
 *                                                                         *
 * This program is free software; you can redistribute it and/or modify    *
 * it under the terms of the GNU General Public License. See the file      *
 * COPYRIGHT for more information.                                         *
 *                                                                         *
 * This program is distributed in the hope that it will be useful,         *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of          *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
 * GNU General Public License for more details.                            *
 *                                                                         *
 * You should have received a copy of the GNU General Public License along *
 * with this program; if not, write to the Free Software Foundation, Inc., *
 * 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA                 *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */


import java.util.*;

/**
 * Symbol table for the interpreter, contains information about
 * variables and functions.
 * 
 * For every binding location of a name a symbol will be created.
 * The symbol tables are connected hierarchically by pointers to
 * the predecessor. Lookup takes predecessors into account.
 */ 
public class SymTab {
  Hashtable h;        // contains the liste of words
                      // key: String, value: SymtabEntry
  
  SymTab pred;  // predecessor symbol table (if exists)

  public SymTab() {
    this(null); 
  }

  public SymTab(SymTab p) {
    h    = new Hashtable();
    pred = p;
  }

  public boolean enter(String s, SymtabEntry e) {
    Object value = lookup(s);
    h.put(s, e);
    return(value==null);
  }

  public SymtabEntry lookup(String s) {
    Object value = h.get(s);
    if (value==null && pred!=null)
      value = pred.lookup(s);
    return ((SymtabEntry)value);
  }

  public String toString() {    // for output with print
    String res    = "symbol table\n=============\n";
    Enumeration e = h.keys();
    String key;
    
    while(e.hasMoreElements()) {
      key = (String)e.nextElement();
      res += key+"   \t"+h.get(key)+"\n";
    }

    if (pred!=null) res+="++ predecessor!\n";
    return(res);
  }

  public int size() {
    return(h.size()); 
  }
}