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Cayenne Object Persistence Framework
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 *  to you under the Apache License, Version 2.0 (the
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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
 * @author Andrus Adamchik
 */
public abstract class NodeDiff implements GraphDiff, Comparable {

    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;
    }

    public boolean isNoop() {
        return false;
    }

    public abstract void apply(GraphChangeHandler tracker);

    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.
     */
    public int compareTo(Object o) {
        if (!(o instanceof NodeDiff)) {
            throw new IllegalArgumentException("Can't compare to " + o);
        }

        return diffId - ((NodeDiff) o).getDiffId();
    }
}