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  package org.apache.cayenne.graph;
  
  /**
   * An abstract superclass of operations on individual nodes and arcs in a
   * digraph.
   * 
   * @since 1.2
   */
  public abstract class NodeDiff implements GraphDiff, Comparable<NodeDiff> {
  
  	private static final long serialVersionUID = -6108147375331011556L;
  	
  	protected int diffId;
  	protected Object nodeId;
  
  	public NodeDiff(Object nodeId) {
  		this.nodeId = nodeId;
  	}
  
  	public NodeDiff(Object nodeId, int diffId) {
  		this.nodeId = nodeId;
  		this.diffId = diffId;
  	}
  
  	@Override
  	public boolean isNoop() {
  		return false;
  	}
  
  	@Override
  	public abstract void apply(GraphChangeHandler tracker);
  
  	@Override
  	public abstract void undo(GraphChangeHandler tracker);
  
  	public Object getNodeId() {
  		return nodeId;
  	}
  
  	/**
  	 * Returns an id of this diff that can be used for various purposes, such as
  	 * identifying the order of the diff in a sequence.
  	 */
  	public int getDiffId() {
  		return diffId;
  	}
  
  	/**
  	 * Sets an id of this diff that can be used for various purposes, such as
  	 * identifying the order of the diff in a sequence.
  	 */
  	public void setDiffId(int diffId) {
  		this.diffId = diffId;
  	}
  
  	/**
  	 * Implements a Comparable interface method to compare based on diffId
  	 * property.
  	 */
  	@Override
  	public int compareTo(NodeDiff o) {
  		return diffId - o.getDiffId();
  	}
  }
  