Package org.geotools.graph.traverse.standard

Class BreadthFirstIterator

  • All Implemented Interfaces:
    GraphIterator
    Direct Known Subclasses:
    DepthFirstIterator, DirectedBreadthFirstIterator
    public class BreadthFirstIterator
extends SourceGraphIterator
    Iterates over the nodes of a graph in a Breadth First Search pattern starting from a specified node. The following illustrates the iteration order.



    The iteration operates by maintaining a node queue of active nodes. An active node is a node that will returned at a later stage of the iteration. The node queue for a Breadth First iteration is implemented as a First In First Out queue. A node is placed in the the node queue if it has not been visited, and it is adjacent to a a node that has been visited. The node queue intially contains only the source node of the traversal.
    Author:
    Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net

    • Constructor Detail

      • BreadthFirstIterator

        public BreadthFirstIterator()

    • Method Detail

      • setSource

        public void setSource​(Graphable source)
        Sets the source of the traversal and places it in the node queue. The first call to this method will result in the internal node queue being built. Subsequent calls to the method clear the node queue and reset the iteration.
        Overrides:
        setSource in class SourceGraphIterator
        Parameters:
        source - The source of the iteration.
        See Also:
        SourceGraphIterator.setSource(Graphable)

      • init

        public void init​(Graph graph,
                 GraphTraversal traversal)
        Does nothing.
        Parameters:
        graph - The graph being whose components are being iterated over.
        See Also:
        org.geotools.graph.traverse.GraphIterator#init(Graph)

      • next

        public Graphable next​(GraphTraversal traversal)
        Returns the next node from the node queue that has not yet been visited. It is possible for the node queue to contain duplicate entries. To prevent the iteration returning the same node multiple times, the visited flag is checked on nodes coming out of the queue. If the flag is set, the node is ignored, not returned, and the next node in the queue is returned. This is however transparent to the caller.
        Returns:
        The next component in the iteration, or null if iteration is complete.
        See Also:
        org.geotools.graph.traverse.GraphIterator#next()

      • cont

        public void cont​(Graphable current,
                 GraphTraversal traversal)
        Looks for nodes adjacent to the current node to place into the node queue. An adjacent node is only placed into the node queue if its visited flag is unset.
        Parameters:
        current - The current component of the traversal.
        See Also:
        org.geotools.graph.traverse.GraphIterator#cont(Graphable)

      • killBranch

        public void killBranch​(Graphable current,
                       GraphTraversal traversal)
        Kills the current branch by not looking for any adjacent nodes to place into the node queue.
        Parameters:
        current - The current component of the traversal.
        See Also:
        org.geotools.graph.traverse.GraphIterator#killBranch(Graphable)

      • buildQueue

        protected Queue<Graphable> buildQueue​(Graph graph)
        Builds the node queue for the iteration.
        Parameters:
        graph - The graph being iterated over.
        Returns:
        A First In First Out queue.

      • getQueue

        protected Queue<Graphable> getQueue()
        Returns the node queue.
        Returns:
        The node queue.