table.java

编译原理大作业---tiger编译器 包括semant,translate,mipsframe,regalloc等所有phase 懂的人自会知道

package Symbol;

class Binder {
  Object value;
  Symbol prevtop;
  Binder tail;
  Binder(Object v, Symbol p, Binder t) { value = v; prevtop = p; tail = t; }
}

/**
 * The Table class is similar to java.util.Dictionary, except that
 * each key must be a Symbol and there is a scope mechanism.
 */

public class Table {

  private java.util.Dictionary dict = new java.util.Hashtable();
  private Symbol top;
  private Binder marks;

  public Table(){}

 /**
  * Gets the object associated with the specified symbol in the Table.
  */
  public Object get(Symbol key) {
    Binder e = (Binder)dict.get(key);
    if (e==null) return null;
    else return e.value;
  }

 /**
  * Puts the specified value into the Table, bound to the specified Symbol.
  */
  public void put(Symbol key, Object value) {
    dict.put(key, new Binder(value, top, (Binder)dict.get(key)));
    top = key;
  }

 /**
  * Remembers the current state of the Table.
  */
  public void beginScope() {marks = new Binder(null,top,marks); top=null;}

 /**
  * Restores the table to what it was at the most recent beginScope
  * that has not already been ended.
  */
  public void endScope() {
    while (top!=null) {
       Binder e = (Binder)dict.get(top);
       if (e.tail!=null) dict.put(top,e.tail);
       else dict.remove(top);
       top = e.prevtop;
    }
    top=marks.prevtop;
    marks=marks.tail;
  }

  /**
   * Returns an enumeration of the Table's symbols.
   */
  public java.util.Enumeration keys() { return dict.keys();}
}