/*
* Copyright (c) 2002-2010 "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 Affero 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.graphdb;
/**
* A client hook for evaluating whether a specific node should be returned from
* a traverser.
* <p>
* When a traverser is created the client parameterizes it with an instance of a
* ReturnableEvaluator. The traverser then invokes the {@link #isReturnableNode
* isReturnableNode()} operation just before returning a specific node, allowing
* the client to either approve or disapprove of returning that node.
* <p>
* When implementing a ReturnableEvaluator, the client investigates the
* information encapsulated in a {@link TraversalPosition} to decide whether a
* node is returnable. For example, here's a snippet detailing a
* ReturnableEvaluator that will return all leaf nodes:
*
* <pre>
* <code>
* ReturnableEvaluator returnEvaluator = new ReturnableEvaluator()
* {
* public boolean {@link #isReturnableNode(TraversalPosition) isReturnableNode}( {@link TraversalPosition TraversalPosition} position )
* {
* // Return nodes that don't have any outgoing relationships,
* // only incoming relationships, i.e. leaf nodes.
* return !position.{@link TraversalPosition#currentNode() currentNode}().{@link Node#hasRelationship(Direction) hasRelationship}(
* {@link Direction#OUTGOING Direction.OUTGOING} );
* }
* };
* </code>
* </pre>
*/
public interface ReturnableEvaluator
{
/**
* A returnable evaluator that returns all nodes encountered.
*/
public static final ReturnableEvaluator ALL = new ReturnableEvaluator()
{
public boolean isReturnableNode( final TraversalPosition currentPosition )
{
return true;
}
};
/**
* A returnable evaluator that returns all nodes except the start node.
*/
public static final ReturnableEvaluator ALL_BUT_START_NODE = new ReturnableEvaluator()
{
public boolean isReturnableNode( final TraversalPosition currentPosition )
{
return currentPosition.notStartNode();
}
};
/**
* Method invoked by traverser to see if the current position is a
* returnable node.
*
* @param currentPos the traversal position
* @return True if current position is a returnable node
*/
public boolean isReturnableNode( TraversalPosition currentPos );
}