org.jgrapht.traverse

Class TopologicalOrderIterator<V,E>

java.lang.Object

org.jgrapht.traverse.AbstractGraphIterator<V,E>

org.jgrapht.traverse.CrossComponentIterator<V,E,java.lang.Object>

org.jgrapht.traverse.TopologicalOrderIterator<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

java.util.Iterator<V>, GraphIterator<V,E>

public class TopologicalOrderIterator<V,E>
extends CrossComponentIterator<V,E,java.lang.Object>

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 KosarajuStrongConnectivityInspector.

Since:

Dec 18, 2004

Constructor Summary

Constructors

Constructor and Description
TopologicalOrderIterator(DirectedGraph<V,E> dg) Creates a new topological order iterator over the directed graph specified, with arbitrary tie-breaking in case of partial order.
TopologicalOrderIterator(DirectedGraph<V,E> dg, java.util.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

Methods inherited from class org.jgrapht.traverse.CrossComponentIterator

getGraph, hasNext, next

Methods inherited from class org.jgrapht.traverse.AbstractGraphIterator

addTraversalListener, isCrossComponentTraversal, isReuseEvents, remove, removeTraversalListener, setCrossComponentTraversal, setReuseEvents

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Detail

TopologicalOrderIterator

public TopologicalOrderIterator(DirectedGraph<V,E> dg)

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.

TopologicalOrderIterator

public TopologicalOrderIterator(DirectedGraph<V,E> dg,
                                java.util.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. 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