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A fork of the Java Cup parser generator with some bug fixes and enhancements. (Forked at version 11b)
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package java_cup;

import java.util.Enumeration;
import java.util.Hashtable;

/**
 * This class represents a set of symbols and provides a series of
 * set operations to manipulate them.
 *
 * @author Scott Hudson
 * @version last updated: 11/25/95
 * @see java_cup.symbol
 */
public class symbol_set {

  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/

    /**
     * Constructor for an empty set.
     */
    public symbol_set() {
    }

    /**
     * Constructor for cloning from another set.
     *
     * @param other the set we are cloning from.
     */
    public symbol_set(symbol_set other) throws internal_error {
        not_null(other);
        _all = (Hashtable) other._all.clone();
    }

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

    /**
     * A hash table to hold the set. Symbols are keyed using their name string.
     */
    protected Hashtable _all = new Hashtable(11);

    /**
     * Access to all elements of the set.
     */
    public Enumeration all() {
        return _all.elements();
    }

    /**
     * size of the set
     */
    public int size() {
        return _all.size();
    }

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

    /**
     * Helper function to test for a null object and throw an exception
     * if one is found.
     *
     * @param obj the object we are testing.
     */
    protected void not_null(Object obj) throws internal_error {
        if (obj == null)
            throw new internal_error("Null object used in set operation");
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Determine if the set contains a particular symbol.
     *
     * @param sym the symbol we are looking for.
     */
    public boolean contains(symbol sym) {
        return _all.containsKey(sym.name());
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Determine if this set is an (improper) subset of another.
     *
     * @param other the set we are testing against.
     */
    public boolean is_subset_of(symbol_set other) throws internal_error {
        not_null(other);

      /* walk down our set and make sure every element is in the other */
        for (Enumeration e = all(); e.hasMoreElements(); )
            if (!other.contains((symbol) e.nextElement()))
                return false;

      /* they were all there */
        return true;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Determine if this set is an (improper) superset of another.
     *
     * @param other the set we are are testing against.
     */
    public boolean is_superset_of(symbol_set other) throws internal_error {
        not_null(other);
        return other.is_subset_of(this);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Add a single symbol to the set.
     *
     * @param sym the symbol we are adding.
     * @return true if this changes the set.
     */
    public boolean add(symbol sym) throws internal_error {
        Object previous;

        not_null(sym);

      /* put the object in */
        previous = _all.put(sym.name(), sym);

      /* if we had a previous, this is no change */
        return previous == null;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Remove a single symbol if it is in the set.
     *
     * @param sym the symbol we are removing.
     */
    public void remove(symbol sym) throws internal_error {
        not_null(sym);
        _all.remove(sym.name());
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Add (union) in a complete set.
     *
     * @param other the set we are adding in.
     * @return true if this changes the set.
     */
    public boolean add(symbol_set other) throws internal_error {
        boolean result = false;

        not_null(other);

      /* walk down the other set and do the adds individually */
        for (Enumeration e = other.all(); e.hasMoreElements(); )
            result = add((symbol) e.nextElement()) || result;

        return result;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Remove (set subtract) a complete set.
     *
     * @param other the set we are removing.
     */
    public void remove(symbol_set other) throws internal_error {
        not_null(other);

      /* walk down the other set and do the removes individually */
        for (Enumeration e = other.all(); e.hasMoreElements(); )
            remove((symbol) e.nextElement());
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Equality comparison.
     */
    public boolean equals(symbol_set other) {
        if (other == null || other.size() != size()) return false;

      /* once we know they are the same size, then improper subset does test */
        try {
            return is_subset_of(other);
        } catch (internal_error e) {
    /* can't throw the error (because super class doesn't), so we crash */
            e.crash();
            return false;
        }
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Generic equality comparison.
     */
    public boolean equals(Object other) {
        if (!(other instanceof symbol_set))
            return false;
        else
            return equals((symbol_set) other);
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Compute a hash code.
     */
    public int hashCode() {
        int result = 0;
        int cnt;
        Enumeration e;

      /* hash together codes from at most first 5 elements */
        for (e = all(), cnt = 0; e.hasMoreElements() && cnt < 5; cnt++)
            result ^= ((symbol) e.nextElement()).hashCode();

        return result;
    }

  /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/

    /**
     * Convert to a string.
     */
    public String toString() {
        String result;
        boolean comma_flag;

        result = "{";
        comma_flag = false;
        for (Enumeration e = all(); e.hasMoreElements(); ) {
            if (comma_flag)
                result += ", ";
            else
                comma_flag = true;

            result += ((symbol) e.nextElement()).name();
        }
        result += "}";

        return result;
    }

  /*-----------------------------------------------------------*/

}