package com.sun.java_cup.internal;
import java.util.Hashtable;
import java.util.Enumeration;
/** This class represents a set of symbols and provides a series of
* set operations to manipulate them.
*
* @see com.sun.java_cup.internal.symbol
* @version last updated: 11/25/95
* @author Scott Hudson
*/
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;
}
/*-----------------------------------------------------------*/
}
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