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  package org.apache.cayenne;
  
  import org.apache.cayenne.graph.GraphEvent;
  
  /**
   * A listener of {@link org.apache.cayenne.DataChannel} lifecycle events. Changes
   * related to an event are attached as a GraphDiff. If a listener needs to process these
   * changes, the easiest way to do that is via GraphChangeHandler "visitor":
   * 
   * <pre>
   *   public void graphChanged(GraphEvent event) {
   *       GraphChangeHandler handler = ..;
   *       event.getDiff().apply(handler);
   *   }
   * </pre>
   * 
   * @since 1.2
   */
  public interface DataChannelListener {
  
      /**
       * Notifies implementing object of the changes that were performed to the object graph
       * externally, not by one of the channel ObjectContexts.
       */
      void graphChanged(GraphEvent event);
  
      /**
       * Notifies implementing object that one of the channel ObjectContexts flushed its
       * changes to the channel.
       */
      void graphFlushed(GraphEvent event);
  
      /**
       * Notifies implementing object that one of the channel ObjectContexts initiated a
       * rollback.
       */
      void graphRolledback(GraphEvent event);
  }
  