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.gene.tetrad.gene.history;
  
  import edu.cmu.tetrad.util.TetradSerializable;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  
  /**
   * Identifies a particular factor (by name) at a particular lag (integer).
   *
   * @author Joseph Ramsey jdramsey@andrew.cmu.edu
   */
  public class LaggedFactor implements Comparable, TetradSerializable {
      static final long serialVersionUID = 23L;
  
      /**
       * The name of the factor.
       *
       * @serial
       */
      private String factor;
  
      /**
       * The number of time steps back for the lagged factor.
       *
       * @serial
       */
      private int lag;
  
      //=============================CONSTRUCTORS==========================//
  
      /**
       * Constructs a new lagged factor with a given name and time lag.
       *
       * @param factor the name of the factor.
       * @param lag    the time lag of the factor.
       */
      public LaggedFactor(String factor, int lag) {
          if (factor == null) {
              throw new NullPointerException("Factor name must not be null");
          }
  
          if (lag < 0) {
              throw new IllegalArgumentException("Lag must be >= 0");
          }
  
          this.factor = factor;
          this.lag = lag;
      }
  
      /**
       * Copy constructor- creates a new object with the same properties as the
       * original
       */
      public LaggedFactor(LaggedFactor orig) {
          this.factor = orig.factor;
          this.lag = orig.lag;
      }
  
      /**
       * Generates a simple exemplar of this class to test serialization.
       *
       * @see edu.cmu.TestSerialization
       * @see edu.cmu.tetradapp.util.TetradSerializableUtils
       */
      public static LaggedFactor serializableInstance() {
          return new LaggedFactor("X", 1);
      }
  
      //=================================PUBLIC METHODS======================//
  
      /**
       * Determines whether the given lagged factor is temporally prior to this
       * lagged factor.
       *
       * @param o an Object, which should be a LaggedFactor.
       * @return this lag minus the given lag, if the lagged factors have the same
       *         name; otherwise, 0.
       */
      public int compareTo(Object o) {
  
          if (o instanceof LaggedFactor) {
              LaggedFactor f = (LaggedFactor) o;
              int n = this.factor.compareTo(f.getFactor());
  
              if (n != 0) {
                  return n;
              }
              else {
                  return this.lag - f.getLag();
              }
          }
          else {
              return 0;
          }
      }
  
      /**
       * Returns the name of the lagged factor.
       *
       * @return this name.
       */
      public String getFactor() {
          return factor;
      }
  
      /**
       * Returns the number of time steps back for this lagged factor.
       *
       * @return the lag.
       */
      public int getLag() {
          return lag;
      }
  
      /**
       * Sets the name of the lagged factor
       */
      public void setFactor(String factor) {
          this.factor = factor;
      }
  
      /**
       * Probably should recheck this later.
       */
      public int hashCode() {
          return 127 * factor.hashCode() + lag;
      }
  
      /**
       * Two lagged factors are equals just in case their factors are equals and
       * their lags are equal.
       */
      public boolean equals(Object o) {
          if (o == this) {
              return true;
          }
          if (!(o instanceof LaggedFactor)) {
              return false;
          }
          LaggedFactor c = (LaggedFactor) o;
          return c.getFactor().equals(this.getFactor()) &&
                  c.getLag() == this.getLag();
      }
  
      /**
       * Returns a string representing this lagged factor.
       *
       * @return this string.
       */
      public String toString() {
          return factor + ":" + lag;
      }
  
      /**
       * Adds semantic checks to the default deserialization method. This method
       * must have the standard signature for a readObject method, and the body of
       * the method must begin with "s.defaultReadObject();". Other than that, any
       * semantic checks can be specified and do not need to stay the same from
       * version to version. A readObject method of this form may be added to any
       * class, even if Tetrad sessions were previously saved out using a version
       * of the class that didn't include it. (That's what the
       * "s.defaultReadObject();" is for. See J. Bloch, Effective Java, for help.
       *
       * @throws java.io.IOException
       * @throws ClassNotFoundException
       */
      private void readObject(ObjectInputStream s)
              throws IOException, ClassNotFoundException {
          s.defaultReadObject();
  
          if (factor == null) {
              throw new NullPointerException();
          }
  
          if (lag < 0) {
              throw new IllegalStateException();
          }
  
      }
  }
  
  
  
  
  
  