Module org.jgrapht.core
Package org.jgrapht.alg.util

Class NeighborCache<V,E>

java.lang.Object
org.jgrapht.alg.util.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 Details

    • NeighborCache

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

  • Method Details

    • 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

    • 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.

    • 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.

    • 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.

    • 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.