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Neo4j kernel is a lightweight, embedded Java database designed to store data structured as graphs rather than tables. For more information, see http://neo4j.org.

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/*
 * Copyright (c) 2002-2015 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j 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 3 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, see .
 */
package org.neo4j.graphdb;

import org.neo4j.graphdb.traversal.Evaluator;
import org.neo4j.graphdb.traversal.TraversalDescription;
import org.neo4j.kernel.Traversal;


/**
 * A client hook for evaluating whether the traverser should traverse beyond a
 * specific node. This is used for pruning the traversal.
 * 
 * When a traverser is created, the client parameterizes it with a
 * StopEvaluator. The traverser then invokes the {@link #isStopNode
 * isStopNode()} operation just before traversing the relationships of a node,
 * allowing the client to either approve or disapprove of traversing beyond that
 * node.
 * 

 * When implementing a StopEvaluator, the client investigates the information
 * encapsulated in a {@link TraversalPosition} to decide whether to block
 * traversal beyond a node or not. For example, here's a snippet detailing a
 * StopEvaluator that blocks traversal beyond a node if it has a certain
 * property value:
 *
 * 
 * 
 * StopEvaluator stopEvaluator = new StopEvaluator()
 * {
 *     // Block traversal if the node has a property with key 'key' and value
 *     // 'someValue'
 *     public boolean {@link #isStopNode(TraversalPosition) isStopNode}( {@link TraversalPosition} position )
 *     {
 *         if ( position.{@link TraversalPosition#isStartNode() isStartNode}() )
 *         {
 *             return false;
 *         }
 *         {@link Node} node = position.{@link TraversalPosition#currentNode() currentNode}();
 *         Object someProp = node.{@link Node#getProperty(String, Object) getProperty}( "key", null );
 *         return someProp instanceof String &&
 *             ((String) someProp).equals( "someValue" );
 *     }
 * };
 * 
 * 
 * @deprecated because of the introduction of a new traversal framework,
 * see more information at {@link TraversalDescription} and
 * {@link Traversal} and the new traversal framework's equivalent
 * {@link Evaluator}.
 */
public interface StopEvaluator
{
    /**
     * Traverse until the end of the graph. This evaluator returns
     * false all the time.
     */
    StopEvaluator END_OF_GRAPH = new StopEvaluator()
    {
        public boolean isStopNode( final TraversalPosition currentPosition )
        {
            return false;
        }
    };

    /**
     * Traverses to depth 1.
     */
    StopEvaluator DEPTH_ONE = new StopEvaluator()
    {
        public boolean isStopNode( final TraversalPosition currentPosition )
        {
            return currentPosition.depth() >= 1;
        }
    };

    /**
     * Method invoked by traverser to see if current position is a stop node.
     *
     * @param currentPos the traversal position
     * @return True if current position is a stop node
     */
    boolean isStopNode( TraversalPosition currentPos );
}