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  package org.apache.cayenne.graph;
  
  /**
   * Defines callback API that can be used by object graph nodes to notify of their state
   * changes. Graph nodes can be any objects as long as each node supports a notion of a
   * unique id within the graph and each directional arc has a unique identifier within its
   * source node.
   * 
   * @since 1.2
   */
  public interface GraphChangeHandler {
  
      /**
       * Notifies implementing object that a node was assigned a new id.
       */
      default void nodeIdChanged(Object nodeId, Object newId) {
      }
  
      /**
       * Notifies implementing object that a new node was created in the graph.
       */
      default void nodeCreated(Object nodeId) {
      }
  
      /**
       * Notifies implementing object that a node was removed from the graph.
       */
      default void nodeRemoved(Object nodeId) {
      }
  
      /**
       * Notifies implementing object that a node's property was modified.
       */
      default void nodePropertyChanged(
              Object nodeId,
              String property,
              Object oldValue,
              Object newValue) {
      }
  
      /**
       * Notifies implementing object that a new arc was created between two nodes.
       */
      default void arcCreated(Object nodeId, Object targetNodeId, ArcId arcId) {
      }
  
      /**
       * Notifies implementing object that an arc between two nodes was deleted.
       */
      default void arcDeleted(Object nodeId, Object targetNodeId, ArcId arcId) {
      }
  }
  