org.jgrapht.graph

Class GraphWalk<V,E>

java.lang.Object

org.jgrapht.graph.GraphWalk<V,E>

Type Parameters:

V - the graph vertex type

E - the graph edge type

All Implemented Interfaces:

GraphPath<V,E>

public class GraphWalk<V,E>
extends Object
implements GraphPath<V,E>

A walk in a graph is an alternating sequence of vertices and edges, starting and ending at a vertex, in which each edge is adjacent in the sequence to its two endpoints. More precisely, a walk is a connected sequence of vertices and edges in a graph $v_0, e_0, v_1, e_1, v_2, \dotso, v_{k-1}, e_{k-1}, v_{k}$, such that for $1 \leq i \leq k$, the edge $e_i$ has endpoints $v_{i-1}$ and $v_i$. The class makes no assumptions with respect to the shape of the walk: edges may be repeated, and the start and end point of the walk may be different.

See http://mathworld.wolfram.com/Walk.html

GraphWalk is the default implementation of GraphPath.

Two special cases exist:

1. A singleton GraphWalk has an empty edge list (the length of the path equals 0), the vertex list contains a single vertex v, and the start and end vertex equal v.
2. An empty Graphwalk has empty edge and vertex lists, and the start and end vertex are both null.

This class is implemented as a light-weight data structure; this class does not verify whether the sequence of edges or the sequence of vertices provided during construction forms an actual walk. It is the responsibility of the invoking class to provide correct input data.

Author:

Joris Kinable

Field Summary

Fields

Modifier and Type	Field and Description
protected List<E>	edgeList
protected V	endVertex
protected Graph<V,E>	graph
protected V	startVertex
protected List<V>	vertexList
protected double	weight

Constructor Summary

Constructors

Constructor and Description
GraphWalk(Graph<V,E> graph, List<V> vertexList, double weight) Creates a walk defined by a sequence of vertices.
GraphWalk(Graph<V,E> graph, V startVertex, V endVertex, List<E> edgeList, double weight) Creates a walk defined by a sequence of edges.
GraphWalk(Graph<V,E> graph, V startVertex, V endVertex, List<V> vertexList, List<E> edgeList, double weight) Creates a walk defined by both a sequence of edges and a sequence of vertices.

Method Summary

Modifier and Type	Method and Description
GraphWalk<V,E>	concat(GraphWalk<V,E> extension, Function<GraphWalk<V,E>,Double> walkWeightCalculator) Concatenates the specified GraphWalk to the end of this GraphWalk.
static <V,E> GraphWalk<V,E>	emptyWalk(Graph<V,E> graph) Convenience method which creates an empty walk.
boolean	equals(Object o)
List<E>	getEdgeList() Returns the edges making up the path.
V	getEndVertex() Returns the end vertex in the path.
Graph<V,E>	getGraph() Returns the graph over which this path is defined.
int	getLength() Returns the length of the path, measured in the number of edges.
V	getStartVertex() Returns the start vertex in the path.
List<V>	getVertexList() Returns the path as a sequence of vertices.
double	getWeight() Returns the weight assigned to the path.
int	hashCode()
boolean	isEmpty() Returns true if the path is an empty path, that is, a path with startVertex=endVertex=null and with an empty vertex and edge list.
GraphWalk<V,E>	reverse() Reverses the direction of the walk.
GraphWalk<V,E>	reverse(Function<GraphWalk<V,E>,Double> walkWeightCalculator) Reverses the direction of the walk.
void	setWeight(double weight) Updates the weight of this walk
static <V,E> GraphWalk<V,E>	singletonWalk(Graph<V,E> graph, V v) Convenience method which creates a walk consisting of a single vertex with weight 0.0.
static <V,E> GraphWalk<V,E>	singletonWalk(Graph<V,E> graph, V v, double weight) Convenience method which creates a walk consisting of a single vertex.
String	toString()
void	verify() Convenience method which verifies whether the given path is feasible wrt the input graph and forms an actual path.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

graph

protected Graph<V,E> graph

vertexList

protected List<V> vertexList

edgeList

protected List<E> edgeList

startVertex

protected V startVertex

endVertex

protected V endVertex

weight

protected double weight

Constructor Detail

GraphWalk

public GraphWalk(Graph<V,E> graph,
                 V startVertex,
                 V endVertex,
                 List<E> edgeList,
                 double weight)

Creates a walk defined by a sequence of edges. A walk defined by its edges can be specified for non-simple graphs. Edge repetition is permitted, the start and end point points ($v_0$ and $v_k$) can be different.

Parameters:

graph - the graph

startVertex - the starting vertex

endVertex - the last vertex of the path

edgeList - the list of edges of the path

weight - the total weight of the path

GraphWalk

public GraphWalk(Graph<V,E> graph,
                 List<V> vertexList,
                 double weight)

Creates a walk defined by a sequence of vertices. Note that the input graph must be simple, otherwise the vertex sequence does not necessarily define a unique path. Furthermore, all vertices must be pairwise adjacent.

Parameters:

graph - the graph

vertexList - the list of vertices of the path

weight - the total weight of the path

GraphWalk

public GraphWalk(Graph<V,E> graph,
                 V startVertex,
                 V endVertex,
                 List<V> vertexList,
                 List<E> edgeList,
                 double weight)

Creates a walk defined by both a sequence of edges and a sequence of vertices. Note that both the sequence of edges and the sequence of vertices must describe the same path! This is not verified during the construction of the walk. This constructor makes it possible to store both a vertex and an edge view of the same walk, thereby saving computational overhead when switching from one to the other.

Parameters:

graph - the graph

startVertex - the starting vertex

endVertex - the last vertex of the path

vertexList - the list of vertices of the path

edgeList - the list of edges of the path

weight - the total weight of the path

Method Detail

getGraph

public Graph<V,E> getGraph()

Description copied from interface: GraphPath

Returns the graph over which this path is defined. The path may also be valid with respect to other graphs.

Specified by:

getGraph in interface GraphPath<V,E>

Returns:

the containing graph

getStartVertex

public V getStartVertex()

Description copied from interface: GraphPath

Returns the start vertex in the path.

Specified by:

getStartVertex in interface GraphPath<V,E>

Returns:

the start vertex

getEndVertex

public V getEndVertex()

Description copied from interface: GraphPath

Returns the end vertex in the path.

Specified by:

getEndVertex in interface GraphPath<V,E>

Returns:

the end vertex

getEdgeList

public List<E> getEdgeList()

Description copied from interface: GraphPath

Returns the edges making up the path. The first edge in this path is incident to the start vertex. The last edge is incident to the end vertex. The vertices along the path can be obtained by traversing from the start vertex, finding its opposite across the first edge, and then doing the same successively across subsequent edges; see GraphPath.getVertexList().

Whether or not the returned edge list is modifiable depends on the path implementation.

Specified by:

getEdgeList in interface GraphPath<V,E>

Returns:

list of edges traversed by the path

getVertexList

public List<V> getVertexList()

Description copied from interface: GraphPath

Returns the path as a sequence of vertices.

Specified by:

getVertexList in interface GraphPath<V,E>

Returns:

path, denoted by a list of vertices

getWeight

public double getWeight()

Description copied from interface: GraphPath

Returns the weight assigned to the path. Typically, this will be the sum of the weights of the edge list entries (as defined by the containing graph), but some path implementations may use other definitions.

Specified by:

getWeight in interface GraphPath<V,E>

Returns:

the weight of the path

setWeight

public void setWeight(double weight)

Updates the weight of this walk

Parameters:

weight - weight of the walk

getLength

public int getLength()

Description copied from interface: GraphPath

Returns the length of the path, measured in the number of edges.

Specified by:

getLength in interface GraphPath<V,E>

Returns:

the length of the path, measured in the number of edges

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

reverse

public GraphWalk<V,E> reverse()

Reverses the direction of the walk. In case of directed/mixed graphs, the arc directions will be reversed. An exception is thrown if reversing an arc $(u,v)$ is impossible because arc $(v,u)$ is not present in the graph. The weight of the resulting walk equals the sum of edge weights in the walk.

Returns:

a reversed GraphWalk

Throws:

org.jgrapht.graph.InvalidGraphWalkException - if the path is invalid

reverse

public GraphWalk<V,E> reverse(Function<GraphWalk<V,E>,Double> walkWeightCalculator)

Reverses the direction of the walk. In case of directed/mixed graphs, the arc directions will be reversed. An exception is thrown if reversing an arc $(u,v)$ is impossible because arc $(v,u)$ is not present in the graph.

Parameters:

walkWeightCalculator - Function used to calculate the weight of the reversed GraphWalk

Returns:

a reversed GraphWalk

Throws:

org.jgrapht.graph.InvalidGraphWalkException - if the path is invalid

concat

public GraphWalk<V,E> concat(GraphWalk<V,E> extension,
                             Function<GraphWalk<V,E>,Double> walkWeightCalculator)

Concatenates the specified GraphWalk to the end of this GraphWalk. This action can only be performed if the end vertex of this GraphWalk is the same as the start vertex of the extending GraphWalk

Parameters:

extension - GraphPath used for the concatenation.

walkWeightCalculator - Function used to calculate the weight of the GraphWalk obtained after the concatenation.

Returns:

a GraphWalk that represents the concatenation of this object's walk followed by the walk specified in the extension argument.

isEmpty

public boolean isEmpty()

Returns true if the path is an empty path, that is, a path with startVertex=endVertex=null and with an empty vertex and edge list.

Returns:

Returns true if the path is an empty path.

verify

public void verify()

Convenience method which verifies whether the given path is feasible wrt the input graph and forms an actual path.

Throws:

org.jgrapht.graph.InvalidGraphWalkException - if the path is invalid

emptyWalk

public static <V,E> GraphWalk<V,E> emptyWalk(Graph<V,E> graph)

Convenience method which creates an empty walk.

Type Parameters:

V - vertex type

E - edge type

Parameters:

graph - input graph

Returns:

an empty walk

singletonWalk

public static <V,E> GraphWalk<V,E> singletonWalk(Graph<V,E> graph,
                                                 V v)

Convenience method which creates a walk consisting of a single vertex with weight 0.0.

Type Parameters:

V - vertex type

E - edge type

Parameters:

graph - input graph

v - single vertex

Returns:

an empty walk

singletonWalk

public static <V,E> GraphWalk<V,E> singletonWalk(Graph<V,E> graph,
                                                 V v,
                                                 double weight)

Convenience method which creates a walk consisting of a single vertex.

Type Parameters:

V - vertex type

E - edge type

Parameters:

graph - input graph

v - single vertex

weight - weight of the path

Returns:

an empty walk