terminal_set.java

package java_cup ;


import java.util.BitSet ;


/**
 * A set of terminals implemented as a bitset.
 * 
 * @version last updated: 11/25/95
 * @author Scott Hudson
 */
public class terminal_set
{
  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/
  /** Constructor for an empty set. */
  public terminal_set ( )
  {
    /* allocate the bitset at what is probably the right size */
    _elements = new BitSet ( terminal.number ( ) ) ;
  }


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


  /*-----------------------------------------------------------*/
  /*--- (Access to) Static (Class) Variables ------------------*/
  /*-----------------------------------------------------------*/
  /** Constant for the empty set. */
  public static final terminal_set EMPTY = new terminal_set ( ) ;


  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/
  /** Bitset to implement the actual set. */
  protected BitSet _elements ;


  /*-----------------------------------------------------------*/
  /*--- General Methods ----------------------------------------*/
  /*-----------------------------------------------------------*/
  /**
   * 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 is empty. */
  public boolean empty ( )
  {
    return equals ( EMPTY ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Determine if the set contains a particular terminal.
   * 
   * @param sym the terminal symbol we are looking for.
   */
  public boolean contains ( terminal sym ) throws internal_error
  {
    not_null ( sym ) ;
    return _elements.get ( sym.index ( ) ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Given its index determine if the set contains a particular terminal.
   * 
   * @param indx the index of the terminal in question.
   */
  public boolean contains ( int indx )
  {
    return _elements.get ( indx ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Determine if this set is an (improper) subset of another.
   * 
   * @param other the set we are testing against.
   */
  public boolean is_subset_of ( terminal_set other ) throws internal_error
  {
    not_null ( other ) ;
    /* make a copy of the other set */
    BitSet copy_other = ( BitSet ) other._elements.clone ( ) ;
    /* and or in */
    copy_other.or ( _elements ) ;
    /* if it hasn't changed, we were a subset */
    return copy_other.equals ( other._elements ) ;
  }


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


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Add a single terminal to the set.
   * 
   * @param sym the terminal being added.
   * @return true if this changes the set.
   */
  public boolean add ( terminal sym ) throws internal_error
  {
    boolean result ;
    not_null ( sym ) ;
    /* see if we already have this */
    result = _elements.get ( sym.index ( ) ) ;
    /* if not we add it */
    if ( ! result ) _elements.set ( sym.index ( ) ) ;
    return result ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Remove a terminal if it is in the set.
   * 
   * @param sym the terminal being removed.
   */
  public void remove ( terminal sym ) throws internal_error
  {
    not_null ( sym ) ;
    _elements.clear ( sym.index ( ) ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Add (union) in a complete set.
   * 
   * @param other the set being added.
   * @return true if this changes the set.
   */
  public boolean add ( terminal_set other ) throws internal_error
  {
    not_null ( other ) ;
    /* make a copy */
    BitSet copy = ( BitSet ) _elements.clone ( ) ;
    /* or in the other set */
    _elements.or ( other._elements ) ;
    /* changed if we are not the same as the copy */
    return ! _elements.equals ( copy ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Determine if this set intersects another.
   * 
   * @param other the other set in question.
   */
  public boolean intersects ( terminal_set other ) throws internal_error
  {
    not_null ( other ) ;
    /* make a copy of the other set */
    BitSet copy = ( BitSet ) other._elements.clone ( ) ;
    /* xor out our values */
    copy.xor ( this._elements ) ;
    /* see if its different */
    return ! copy.equals ( other._elements ) ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** Equality comparison. */
  public boolean equals ( terminal_set other )
  {
    if ( other == null )
      return false ;
    else return _elements.equals ( other._elements ) ;
  }


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


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** Convert to string. */
  public String toString ( )
  {
    String result ;
    boolean comma_flag ;
    result = "{" ;
    comma_flag = false ;
    for ( int t = 0 ; t < terminal.number ( ) ; t ++ )
    {
      if ( _elements.get ( t ) )
      {
        if ( comma_flag )
          result += ", " ;
        else comma_flag = true ;
        result += terminal.find ( t ).name ( ) ;
      }
    }
    result += "}" ;
    return result ;
  }
  /*-----------------------------------------------------------*/
}