org.jgrapht.alg.util

## Class NeighborCache<V,E>

• Type Parameters:
V - the vertex type
E - the edge type
All Implemented Interfaces:
EventListener, GraphListener<V,E>, VertexSetListener<V>

public class NeighborCache<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.

The cache also keeps track of successors and predecessors for each vertex. This means that the result of the union of calling predecessorsOf(v) and successorsOf(v) is equal to the result of calling neighborsOf(v) for a given vertex v.

Author:
Szabolcs Besenyei
• ### Constructor Summary

Constructors
Constructor and Description
NeighborCache(Graph<V,E> graph)
Constructor
• ### Method Summary

All 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 unique neighbors of the given vertex if it exists in the cache, otherwise it is initialized.
Set<V> predecessorsOf(V v)
Returns the unique predecessors of the given vertex if it exists in the cache, otherwise it is initialized.
Set<V> successorsOf(V v)
Returns the unique successors of the given vertex if it exists in the cache, otherwise it is initialized.
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
• ### Methods inherited from interface org.jgrapht.event.GraphListener

edgeWeightUpdated
• ### Constructor Detail

• #### NeighborCache

public NeighborCache(Graph<V,E> graph)
Constructor
Parameters:
graph - the input graph
Throws:
NullPointerException - if the input graph is null
• ### Method Detail

• #### predecessorsOf

public Set<V> predecessorsOf(V v)
Returns the unique predecessors of the given vertex if it exists in the cache, otherwise it is initialized.
Parameters:
v - the given vertex
Returns:
the unique predecessors of the given vertex
• #### successorsOf

public Set<V> successorsOf(V v)
Returns the unique successors of the given vertex if it exists in the cache, otherwise it is initialized.
Parameters:
v - the given vertex
Returns:
the unique successors of the given vertex
• #### neighborsOf

public Set<V> neighborsOf(V v)
Returns the unique neighbors of the given vertex if it exists in the cache, otherwise it is initialized.
Parameters:
v - the given vertex
Returns:
the unique neighbors of the given 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(V) unless duplicate neighbors are important.
Parameters:
v - the vertex whose neighbors are desired
Returns:
all neighbors of the specified vertex

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.
• #### 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.

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.
• #### 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.