code: ///////////////////////////////////////////////////////////////////////////////
  // For information as to what this class does, see the Javadoc, below.       //
  // Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,       //
  // 2007, 2008, 2009, 2010, 2014, 2015 by Peter Spirtes, Richard Scheines, Joseph   //
  // Ramsey, and Clark Glymour.                                                //
  //                                                                           //
  // This program is free software; you can redistribute it and/or modify      //
  // it under the terms of the GNU General Public License as published by      //
  // the Free Software Foundation; either version 2 of the License, or         //
  // (at your option) any later version.                                       //
  //                                                                           //
  // This program is distributed in the hope that it will be useful,           //
  // but WITHOUT ANY WARRANTY; without even the implied warranty of            //
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the             //
  // GNU General Public License for more details.                              //
  //                                                                           //
  // You should have received a copy of the GNU General Public License         //
  // along with this program; if not, write to the Free Software               //
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA //
  ///////////////////////////////////////////////////////////////////////////////
  
  package edu.cmu.tetrad.data;
  
  import edu.cmu.tetrad.graph.Node;
  import edu.cmu.tetrad.util.TetradSerializable;
  
  /**
   * Interface implemented by classes, instantiations of which are capable of
   * serving as variables for columns in a DataSet. Such a class provides needed
   * details as to how the data in its column are to be interpreted. In
   * particular, a variable has a name and specifies a value in the column that is
   * to be interpreted as a missing datum. The variable also specifies how
   * external data (in String form, say) is to be converted into raw data of the
   * type used in the column in question.
   *
   * @author Joseph Ramsey
   */
  public interface Variable extends Node, TetradSerializable {
  
      /**
       * Required serial version UID for serialization. Must be 23L.
       */
      long serialVersionUID = 23L;
  
      /**
       * @return the missing value marker as an object--i.e. a double if
       * continuous, an Integer if discrete, etc.
       */
      Object getMissingValueMarker();
  
      /**
       * Tests whether the given value is the missing data marker.
       *
       * @param value The object value one wants to check as a missing value.
       * @return true iff the given object is equals to <code>getMissingValueMarker()</code>.
       */
      boolean isMissingValue(Object value);
  
      /**
       * Checks to see whether the passed value can be converted into a
       * value for this variable.
       *
       * @param value The object value to be checked. For instance, for a
       *              continuous variable, this would be a Double, for a discrete
       *              variable, and Integer, etc.
       * @return true iff the object is a valid value for this variable.
       */
      boolean checkValue(Object value);
  }
  
  
  
  
  
  