org.jscience.computing.graph.iterators
Class ClosestFirstIterator

java.lang.Object
  extended by org.jscience.computing.graph.iterators.AbstractGraphIterator
      extended by org.jscience.computing.graph.iterators.CrossComponentIterator
          extended by org.jscience.computing.graph.iterators.ClosestFirstIterator
All Implemented Interfaces:
java.util.Iterator, GraphIterator

public class ClosestFirstIterator
extends CrossComponentIterator

A closest-first iterator for a directed or undirected graph. For this iterator to work correctly the graph must not be modified during iteration. Currently there are no means to ensure that, nor to fail-fast. The results of such modifications are undefined.

The metric for closest here is the path length from a start vertex. Edge.getWeight() is summed to calculate path length. Negative edge weights will result in an IllegalArgumentException. Optionally, path length may be bounded by a finite radius.

Since:
Sep 2, 2003

Constructor Summary
ClosestFirstIterator(Graph g)
          Creates a new closest-first iterator for the specified graph.
ClosestFirstIterator(Graph g, java.lang.Object startVertex)
          Creates a new closest-first iterator for the specified graph.
ClosestFirstIterator(Graph g, java.lang.Object startVertex, double radius)
          Creates a new radius-bounded closest-first iterator for the specified graph.
 
Method Summary
protected  void encounterVertex(java.lang.Object vertex, Edge edge)
          Update data structures the first time we see a vertex.
protected  void encounterVertexAgain(java.lang.Object vertex, Edge edge)
          Override superclass.
 double getShortestPathLength(java.lang.Object vertex)
          Get the length of the shortest path known to the given vertex.
 Edge getSpanningTreeEdge(java.lang.Object vertex)
          Get the spanning tree edge reaching a vertex which has been seen already in this traversal.
protected  boolean isConnectedComponentExhausted()
          Returns true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
protected  java.lang.Object provideNextVertex()
          Returns the vertex to be returned in the following call to the iterator next method.
 void setCrossComponentTraversal(boolean crossComponentTraversal)
          Sets the cross component traversal flag - indicates whether to traverse the graph across connected components.
 
Methods inherited from class org.jscience.computing.graph.iterators.CrossComponentIterator
getSeenData, hasNext, isSeenVertex, next, putSeenData
 
Methods inherited from class org.jscience.computing.graph.iterators.AbstractGraphIterator
addTraversalListener, fireConnectedComponentFinished, fireConnectedComponentStarted, fireEdgeTraversed, fireVertexTraversed, isCrossComponentTraversal, isReuseEvents, remove, removeTraversalListener, setReuseEvents
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

ClosestFirstIterator

public ClosestFirstIterator(Graph g)
Creates a new closest-first iterator for the specified graph.

Parameters:
g - the graph to be iterated.

ClosestFirstIterator

public ClosestFirstIterator(Graph g,
                            java.lang.Object startVertex)
Creates a new closest-first iterator for the specified graph. Iteration will start at the specified start vertex and will be limited to the connected component that includes that vertex. If the specified start vertex is null, iteration will start at an arbitrary vertex and will not be limited, that is, will be able to traverse all the graph.

Parameters:
g - the graph to be iterated.
startVertex - the vertex iteration to be started.

ClosestFirstIterator

public ClosestFirstIterator(Graph g,
                            java.lang.Object startVertex,
                            double radius)
Creates a new radius-bounded closest-first iterator for the specified graph. Iteration will start at the specified start vertex and will be limited to the subset of the connected component which includes that vertex and is reachable via paths of length less than or equal to the specified radius. The specified start vertex may not be null.

Parameters:
g - the graph to be iterated.
startVertex - the vertex iteration to be started.
radius - limit on path length, or Double.POSITIVE_INFINITY for unbounded search.
Method Detail

setCrossComponentTraversal

public void setCrossComponentTraversal(boolean crossComponentTraversal)
Description copied from class: AbstractGraphIterator
Sets the cross component traversal flag - indicates whether to traverse the graph across connected components.

Overrides:
setCrossComponentTraversal in class AbstractGraphIterator
Parameters:
crossComponentTraversal - if true traverses across connected components.

getShortestPathLength

public double getShortestPathLength(java.lang.Object vertex)
Get the length of the shortest path known to the given vertex. If the vertex has already been visited, then it is truly the shortest path length; otherwise, it is the best known upper bound.

Parameters:
vertex - vertex being sought from start vertex
Returns:
length of shortest path known, or Double.POSITIVE_INFINITY if no path found yet

getSpanningTreeEdge

public Edge getSpanningTreeEdge(java.lang.Object vertex)
Get the spanning tree edge reaching a vertex which has been seen already in this traversal. This edge is the last link in the shortest known path between the start vertex and the requested vertex. If the vertex has already been visited, then it is truly the minimum spanning tree edge; otherwise, it is the best candidate seen so far.

Parameters:
vertex - the spanned vertex.
Returns:
the spanning tree edge, or null if the vertex either has not been seen yet or is the start vertex.

isConnectedComponentExhausted

protected boolean isConnectedComponentExhausted()
Description copied from class: CrossComponentIterator
Returns true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.

Specified by:
isConnectedComponentExhausted in class CrossComponentIterator
Returns:
true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
See Also:
CrossComponentIterator.isConnectedComponentExhausted()

encounterVertex

protected void encounterVertex(java.lang.Object vertex,
                               Edge edge)
Description copied from class: CrossComponentIterator
Update data structures the first time we see a vertex.

Specified by:
encounterVertex in class CrossComponentIterator
Parameters:
vertex - the vertex encountered
edge - the edge via which the vertex was encountered, or null if the vertex is a starting point
See Also:
CrossComponentIterator.encounterVertex(java.lang.Object, org.jscience.computing.graph.Edge)

encounterVertexAgain

protected void encounterVertexAgain(java.lang.Object vertex,
                                    Edge edge)
Override superclass. When we see a vertex again, we need to see if the new edge provides a shorter path than the old edge.

Specified by:
encounterVertexAgain in class CrossComponentIterator
Parameters:
vertex - the vertex re-encountered
edge - the edge via which the vertex was re-encountered

provideNextVertex

protected java.lang.Object provideNextVertex()
Description copied from class: CrossComponentIterator
Returns the vertex to be returned in the following call to the iterator next method.

Specified by:
provideNextVertex in class CrossComponentIterator
Returns:
the next vertex to be returned by this iterator.
See Also:
CrossComponentIterator.provideNextVertex()