// FILE. . . . . /home/hak/hlt/src/hlt/osfv1/base/Feature.java
// EDIT BY . . . Hassan Ait-Kaci
// ON MACHINE. . Hak-Laptop
// STARTED ON. . Mon Sep 02 09:13:47 2013

/**
 * This is the class of &psi;-term fearures as explained in the <a
 * href="../specs/basic.html#features">specification</a>.
 *
 * @version     Last modified on Mon Sep 02 09:13:58 2013 by hak
 * @author      <a href="mailto:hak@acm.org">Hassan A&iuml;t-Kaci</a>
 * @copyright   &copy; <a href="http://www.hassan-ait-kaci.net/">by the author</a>
 */

package hlt.osf.base;

import java.util.HashMap;

public class Feature
  {
    /* ************************************************************************ */

    /**
     * This is a global hash map associating a feature name to the unique
     * feature bearing this name.
     */
    private static HashMap _knownFeatures = new HashMap();

    /**
     * This static method returns the feature with the given name. If the
     * given name is null, a new feature is created and its newly created
     * name associated to it. Therefore, this class has no public
     * constructor. The only way to access or make a feature is by invoking
     * the method <tt>Feature.getFeature(String name)</tt> with name identifying
     * the feature (if <tt>null</tt>, a feature with a newly generated name is
     * created and returned).
     */
    public static Feature getFeature (String name) throws BadFeatureNameException
      {
	if (name == null)
	  throw new BadFeatureNameException("null feature name");

	name = name.intern();
	  
	Feature feature = (Feature)_knownFeatures.get(name);

	if (feature == null)
	  {
	    feature = new Feature(name);
	    _knownFeatures.put(feature.name(),feature);
	  }

	return feature;
      }

    /* ************************************************************************ */

    private Feature (String name)
      {
	_name = name;
      }

    /* ************************************************************************ */

    private String _name;

    public String name ()
      {
	return _name;
      }

    /* ************************************************************************ */

    // It is not necessary to change the equals method: we can let it
    // remain == since equals features are always uniquely identified.

    // public boolean equals (Object other)
    // {
    //   return (other instanceof Feature && _name == ((Feature)other).name());
    // }

    public int hashCode ()
      {
	return _name.hashCode();
      }

    /* ************************************************************************ */

    /**
     * Return a string value for this feature, which is its name.
     */
    public String toString ()
      {
	return name();
      }

    /* ************************************************************************ */
  }