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.session;
  
  import javax.swing.*;
  import java.beans.PropertyChangeEvent;
  import java.beans.PropertyChangeListener;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Allows editors launched for session nodes to register that relevant changes
   * have been made that will require models downstream to be reconstructed.
   *
   * @author William Taysom
   * @author Joseph Ramsey
   */
  public final class ModificationRegistery {
      private static final Set<Object> EDITED_MODELS = new HashSet<>();
      private static final Map<JComponent, SessionNode> EDITORS_TO_SESSION_NODES = new HashMap<>();
      private static final Map<JComponent, PropertyChangeListener> EDITORS_TO_LISTENERS = new HashMap<>();
  
      /**
       * Registers an editor which could modify model.
       */
      public static void registerEditor(SessionNode sessionNode,
                                        JComponent editor) {
          if (editor == null) {
              throw new NullPointerException();
          }
  
          if (sessionNode == null) {
              throw new NullPointerException();
          }
  
          if (editor instanceof DelegatesEditing) {
              editor = ((DelegatesEditing) editor).getEditDelegate();
          }
  
          EDITORS_TO_SESSION_NODES.put(editor, sessionNode);
  
          PropertyChangeListener listener = new PropertyChangeListener() {
              public void propertyChange(PropertyChangeEvent evt) {
                  if ("modelChanged".equals(evt.getPropertyName())) {
                      JComponent editor = (JComponent) evt.getSource();
                      Object sessionNode = EDITORS_TO_SESSION_NODES.get(editor);
                      if (sessionNode != null) {
                          EDITED_MODELS.add(sessionNode);
                      }
                  }
              }
          };
  
          editor.addPropertyChangeListener(listener);
          EDITORS_TO_LISTENERS.put(editor, listener);
      }
  
      /**
       * @return true if an editor has registered that model has changed.
       */
      public static boolean modelHasChanged(SessionNode sessionNode) {
          return EDITED_MODELS.contains(sessionNode);
      }
  
      public static void unregisterEditor(JComponent editor) {
          if (editor instanceof DelegatesEditing) {
              editor = ((DelegatesEditing) editor).getEditDelegate();
          }
  
          EDITORS_TO_SESSION_NODES.remove(editor);
          PropertyChangeListener listener =
                  EDITORS_TO_LISTENERS.get(editor);
          editor.removePropertyChangeListener(listener);
          EDITORS_TO_LISTENERS.remove(editor);
      }
  
      /**
       * Removes the given session node from the list of sessions nodes for which
       * changes have been made.
       */
      public static void unregisterSessionNode(SessionNode sessionNode) {
          EDITED_MODELS.remove(sessionNode);
      }
  }
  
  
  
  
  