org.jgrapht.alg

Class NeighborIndex<V,E>

java.lang.Object

org.jgrapht.alg.NeighborIndex<V,E>

All Implemented Interfaces:

EventListener, GraphListener<V,E>, VertexSetListener<V>

public class NeighborIndex<V,E>
extends Object
implements GraphListener<V,E>

Maintains a cache of each vertex's neighbors. While lists of neighbors can be obtained from Graphs, they are re-calculated at each invocation by walking a vertex's incident edges, which becomes inordinately expensive when performed often.

Edge direction is ignored when evaluating neighbors; to take edge direction into account when indexing neighbors, use DirectedNeighborIndex.

A vertex's neighbors are cached the first time they are asked for (i.e. the index is built on demand). The index will only be updated automatically if it is added to the associated graph as a listener. If it is added as a listener to a graph other than the one it indexes, results are undefined.

Since:

Dec 13, 2005

Author:

Charles Fry

Constructor Summary

Constructors

Constructor and Description
NeighborIndex(Graph<V,E> g) Creates a neighbor index for the specified undirected graph.

Method Summary

Methods

Modifier and Type	Method and Description
void	edgeAdded(GraphEdgeChangeEvent<V,E> e) Notifies that an edge has been added to the graph.
void	edgeRemoved(GraphEdgeChangeEvent<V,E> e) Notifies that an edge has been removed from the graph.
List<V>	neighborListOf(V v) Returns a list of vertices which are adjacent to a specified vertex.
Set<V>	neighborsOf(V v) Returns the set of vertices which are adjacent to a specified vertex.
void	vertexAdded(GraphVertexChangeEvent<V> e) Notifies that a vertex has been added to the graph.
void	vertexRemoved(GraphVertexChangeEvent<V> e) Notifies that a vertex has been removed from the graph.

Methods inherited from class java.lang.Object

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

Constructor Detail

NeighborIndex

public NeighborIndex(Graph<V,E> g)

Creates a neighbor index for the specified undirected graph.

Parameters:

g - the graph for which a neighbor index is to be created.

Method Detail

neighborsOf

public Set<V> neighborsOf(V v)

Returns the set of vertices which are adjacent to a specified vertex. The returned set is backed by the index, and will be updated when the graph changes as long as the index has been added as a listener to the graph.

Parameters:

v - the vertex whose neighbors are desired

Returns:

all unique neighbors of the specified vertex

neighborListOf

public List<V> neighborListOf(V v)

Returns a list of vertices which are adjacent to a specified vertex. If the graph is a multigraph, vertices may appear more than once in the returned list. Because a list of neighbors can not be efficiently maintained, it is reconstructed on every invocation, by duplicating entries in the neighbor set. It is thus more efficient to use neighborsOf(Object) unless duplicate neighbors are important.

Parameters:

v - the vertex whose neighbors are desired

Returns:

all neighbors of the specified vertex

edgeAdded

public void edgeAdded(GraphEdgeChangeEvent<V,E> e)

Description copied from interface: GraphListener

Notifies that an edge has been added to the graph.

Specified by:

edgeAdded in interface GraphListener<V,E>

Parameters:

e - the edge event.

See Also:

GraphListener.edgeAdded(GraphEdgeChangeEvent)

edgeRemoved

public void edgeRemoved(GraphEdgeChangeEvent<V,E> e)

Description copied from interface: GraphListener

Notifies that an edge has been removed from the graph.

Specified by:

edgeRemoved in interface GraphListener<V,E>

Parameters:

e - the edge event.

See Also:

GraphListener.edgeRemoved(GraphEdgeChangeEvent)

vertexAdded

public void vertexAdded(GraphVertexChangeEvent<V> e)

Description copied from interface: VertexSetListener

Notifies that a vertex has been added to the graph.

Specified by:

vertexAdded in interface VertexSetListener<V>

Parameters:

e - the vertex event.

See Also:

VertexSetListener.vertexAdded(GraphVertexChangeEvent)

vertexRemoved

public void vertexRemoved(GraphVertexChangeEvent<V> e)

Description copied from interface: VertexSetListener

Notifies that a vertex has been removed from the graph.

Specified by:

vertexRemoved in interface VertexSetListener<V>

Parameters:

e - the vertex event.

See Also:

VertexSetListener.vertexRemoved(GraphVertexChangeEvent)