org.jscience.computing.graph.iterators
Class TopologicalOrderIterator

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.TopologicalOrderIterator
All Implemented Interfaces:
java.util.Iterator, GraphIterator

public class TopologicalOrderIterator
extends CrossComponentIterator

Implements topological order traversal for a directed graph. A topological sort is a permutation p of the vertices of a graph such that an edge (i,j) implies that i appears before j in p (Skiena 1990, p. 208). See also http://mathworld.wolfram.com/TopologicalSort.html.

See "Algorithms in Java, Third Edition, Part 5: Graph Algorithms" by Robert Sedgewick and "Data Structures and Algorithms with Object-Oriented Design Patterns in Java" by Bruno R. Preiss for implementation alternatives. The latter can be found online at http://www.brpreiss.com/books/opus5/

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.

Since:
Dec 18, 2004

Constructor Summary
TopologicalOrderIterator(DirectedGraph dg)
          Creates a new topological order iterator over the directed graph specified.
 
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)
          Called whenever we re-encounter a vertex.
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.
 
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, setCrossComponentTraversal, setReuseEvents
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

TopologicalOrderIterator

public TopologicalOrderIterator(DirectedGraph dg)
Creates a new topological order iterator over the directed graph specified. Traversal will start at one of the graphs sources. See the definition of source at http://mathworld.wolfram.com/Source.html.

Parameters:
dg - the directed graph to be iterated.
Method Detail

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(Object,Edge)

encounterVertexAgain

protected void encounterVertexAgain(java.lang.Object vertex,
                                    Edge edge)
Description copied from class: CrossComponentIterator
Called whenever we re-encounter a vertex. The default implementation does nothing.

Specified by:
encounterVertexAgain in class CrossComponentIterator
Parameters:
vertex - the vertex re-encountered
edge - the edge via which the vertex was re-encountered
See Also:
CrossComponentIterator.encounterVertexAgain(Object,Edge)

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()