Package org.jgrapht.traverse
Class TopologicalOrderIterator<V,E>
java.lang.Object
org.jgrapht.traverse.AbstractGraphIterator<V,E>
org.jgrapht.traverse.CrossComponentIterator<V,E,Object>
org.jgrapht.traverse.TopologicalOrderIterator<V,E>
- All Implemented Interfaces:
Iterator<V>
,GraphIterator<V,
E>
Implements topological order traversal for a directed acyclic 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 be acyclic, and must
not be modified during iteration. Currently there are no means to ensure
that, nor to fail-fast; the results with cyclic input (including self-loops)
or concurrent modifications are undefined. To precheck a graph for cycles,
consider using CycleDetector
or StrongConnectivityInspector
.
- Since:
- Dec 18, 2004
- Author:
- Marden Neubert
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Nested Class Summary
Nested classes/interfaces inherited from class org.jgrapht.traverse.CrossComponentIterator
CrossComponentIterator.VisitColor
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Field Summary
Fields inherited from class org.jgrapht.traverse.AbstractGraphIterator
nListeners
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Constructor Summary
ConstructorsConstructorDescriptionCreates a new topological order iterator over the directed graph specified, with arbitrary tie-breaking in case of partial order.TopologicalOrderIterator
(DirectedGraph<V, E> dg, Queue<V> queue) Creates a new topological order iterator over the directed graph specified, with a user-supplied queue implementation to allow customized control over tie-breaking in case of partial order. -
Method Summary
Modifier and TypeMethodDescriptionprotected void
encounterVertex
(V vertex, E edge) Update data structures the first time we see a vertex.protected void
encounterVertexAgain
(V vertex, E edge) Called whenever we re-encounter a vertex.protected boolean
Returns true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.protected V
Returns the vertex to be returned in the following call to the iteratornext
method.Methods inherited from class org.jgrapht.traverse.CrossComponentIterator
finishVertex, getGraph, getSeenData, hasNext, isSeenVertex, next, putSeenData
Methods inherited from class org.jgrapht.traverse.AbstractGraphIterator
addTraversalListener, fireConnectedComponentFinished, fireConnectedComponentStarted, fireEdgeTraversed, fireVertexFinished, 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
Methods inherited from interface java.util.Iterator
forEachRemaining
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Constructor Details
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TopologicalOrderIterator
Creates a new topological order iterator over the directed graph specified, with arbitrary tie-breaking in case of partial order. Traversal will start at one of the graph's sources. See the definition of source at http://mathworld.wolfram.com/Source.html.- Parameters:
dg
- the directed graph to be iterated.
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TopologicalOrderIterator
Creates a new topological order iterator over the directed graph specified, with a user-supplied queue implementation to allow customized control over tie-breaking in case of partial order. Traversal will start at one of the graph's sources. See the definition of source at http://mathworld.wolfram.com/Source.html.- Parameters:
dg
- the directed graph to be iterated.queue
- queue to use for tie-break in case of partial order (e.g. a PriorityQueue can be used to break ties according to vertex priority); must be initially empty
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Method Details
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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 classCrossComponentIterator<V,
E, Object> - Returns:
- true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
- See Also:
-
encounterVertex
Description copied from class:CrossComponentIterator
Update data structures the first time we see a vertex.- Specified by:
encounterVertex
in classCrossComponentIterator<V,
E, Object> - Parameters:
vertex
- the vertex encounterededge
- the edge via which the vertex was encountered, or null if the vertex is a starting point- See Also:
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encounterVertexAgain
Description copied from class:CrossComponentIterator
Called whenever we re-encounter a vertex. The default implementation does nothing.- Specified by:
encounterVertexAgain
in classCrossComponentIterator<V,
E, Object> - Parameters:
vertex
- the vertex re-encounterededge
- the edge via which the vertex was re-encountered- See Also:
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provideNextVertex
Description copied from class:CrossComponentIterator
Returns the vertex to be returned in the following call to the iteratornext
method.- Specified by:
provideNextVertex
in classCrossComponentIterator<V,
E, Object> - Returns:
- the next vertex to be returned by this iterator.
- See Also:
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