Type Parameters:
V - the graph vertex type
E - the graph edge type
All Implemented Interfaces:
Iterator<V>, GraphIterator<V,E>

A breadth-first iterator for a directed or undirected graph.

For this iterator to work correctly the graph must not be modified during iteration. Currently there are no means to ensure that, nor to fail-fast. The results of such modifications are undefined.

Author:
Barak Naveh
• Nested Class Summary

Nested Classes
Modifier and Type
Class
Description
protected static class
BreadthFirstIterator.SearchNodeData<E>
Data kept for discovered vertices.
• Field Summary

Fields inherited from class org.jgrapht.traverse.AbstractGraphIterator

crossComponentTraversal, graph, nListeners, reusableEdgeEvent, reusableVertexEvent, reuseEvents
• Constructor Summary

Constructors
Constructor
Description
BreadthFirstIterator(Graph<V,E> g)
Creates a new breadth-first iterator for the specified graph.
BreadthFirstIterator(Graph<V,E> g, Iterable<V> startVertices)
Creates a new breadth-first iterator for the specified graph.
BreadthFirstIterator(Graph<V,E> g, V startVertex)
Creates a new breadth-first iterator for the specified graph.
• Method Summary

Modifier and Type
Method
Description
protected void
encounterVertex(V vertex, E edge)
Update data structures the first time we see a vertex.
protected void
encounterVertexAgain(V vertex, E edge)
Called whenever we re-encounter a vertex.
int
getDepth(V v)
Returns the depth of vertex $v$ in the search tree.
V
getParent(V v)
Returns the parent node of vertex $v$ in the BFS search tree, or null if $v$ is the root node.
E
getSpanningTreeEdge(V v)
Returns the edge connecting vertex $v$ to its parent in the spanning tree formed by the BFS search, or null if $v$ is a root node.
protected boolean
isConnectedComponentExhausted()
Returns true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
protected V
provideNextVertex()
Returns the vertex to be returned in the following call to the iterator next method.

Methods inherited from class org.jgrapht.traverse.CrossComponentIterator

finishVertex, getEntireGraphVertexIterator, getSeenData, hasNext, isSeenVertex, next, putSeenData, selectOutgoingEdges

Methods inherited from class org.jgrapht.traverse.AbstractGraphIterator

addTraversalListener, createEdgeTraversalEvent, createVertexTraversalEvent, fireConnectedComponentFinished, fireConnectedComponentStarted, fireEdgeTraversed, fireVertexFinished, fireVertexTraversed, getGraph, isCrossComponentTraversal, isReuseEvents, remove, removeTraversalListener, setCrossComponentTraversal, setReuseEvents

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

forEachRemaining
• Constructor Details

Creates a new breadth-first iterator for the specified graph.
Parameters:
g - the graph to be iterated.

Creates a new breadth-first iterator for the specified graph. Iteration will start at the specified start vertex and will be limited to the connected component that includes that vertex. If the specified start vertex is null, iteration will start at an arbitrary vertex and will not be limited, that is, will be able to traverse all the graph.
Parameters:
g - the graph to be iterated.
startVertex - the vertex iteration to be started.

Creates a new breadth-first iterator for the specified graph. Iteration will start at the specified start vertices and will be limited to the connected component that includes those vertices. If the specified start vertices is null, iteration will start at an arbitrary vertex and will not be limited, that is, will be able to traverse all the graph.
Parameters:
g - the graph to be iterated.
startVertices - the vertices iteration to be started.
• Method Details

• isConnectedComponentExhausted

protected boolean isConnectedComponentExhausted()
Returns true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
Specified by:
isConnectedComponentExhausted in class CrossComponentIterator<V,E,BreadthFirstIterator.SearchNodeData<E>>
Returns:
true if there are no more uniterated vertices in the currently iterated connected component; false otherwise.
• encounterVertex

protected void encounterVertex(V vertex, E edge)
Update data structures the first time we see a vertex.
Specified by:
encounterVertex in class CrossComponentIterator<V,E,BreadthFirstIterator.SearchNodeData<E>>
Parameters:
vertex - the vertex encountered
edge - the edge via which the vertex was encountered, or null if the vertex is a starting point
• encounterVertexAgain

protected void encounterVertexAgain(V vertex, E edge)
Called whenever we re-encounter a vertex. The default implementation does nothing.
Specified by:
encounterVertexAgain in class CrossComponentIterator<V,E,BreadthFirstIterator.SearchNodeData<E>>
Parameters:
vertex - the vertex re-encountered
edge - the edge via which the vertex was re-encountered
• getParent

public V getParent(V v)
Returns the parent node of vertex $v$ in the BFS search tree, or null if $v$ is the root node. This method can only be invoked on a vertex $v$ once the iterator has visited vertex $v$!
Parameters:
v - vertex
Returns:
parent node of vertex $v$ in the BFS search tree, or null if $v$ is a root node
• getSpanningTreeEdge

public E getSpanningTreeEdge(V v)
Returns the edge connecting vertex $v$ to its parent in the spanning tree formed by the BFS search, or null if $v$ is a root node. This method can only be invoked on a vertex $v$ once the iterator has visited vertex $v$!
Parameters:
v - vertex
Returns:
edge connecting vertex $v$ in the BFS search tree to its parent, or null if $v$ is a root node
• getDepth

public int getDepth(V v)
Returns the depth of vertex $v$ in the search tree. The depth of a vertex $v$ is defined as the number of edges traversed on the path from the root of the BFS tree to vertex $v$. The root of the search tree has depth 0. This method can only be invoked on a vertex $v$ once the iterator has visited vertex $v$!
Parameters:
v - vertex
Returns:
depth of vertex $v$ in the search tree
• provideNextVertex

protected V provideNextVertex()
Description copied from class: CrossComponentIterator
Returns the vertex to be returned in the following call to the iterator next method.
Specified by:
provideNextVertex in class CrossComponentIterator<V,E,BreadthFirstIterator.SearchNodeData<E>>
Returns:
the next vertex to be returned by this iterator.