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

    java.lang.Object
      org.jgrapht.alg.NeighborIndex<V,E>

All Implemented Interfaces:
  java.util.EventListener, GraphListener<V,E>, VertexSetListener<V>

    public class NeighborIndex<V,E>

extends java.lang.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
`NeighborIndex(Graph<V,E> g)` Creates a neighbor index for the specified undirected graph.

Method Summary
`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.
`java.util.List<V>` | `neighborListOf(V v)` Returns a list of vertices which are adjacent to a specified vertex.
`java.util.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 java.util.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 java.util.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)`

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