org.jgrapht.graph

Class Subgraph<V,E,G extends Graph<V,E>>

• Type Parameters:
V - the vertex type
E - the edge type
G - the type of the base graph
All Implemented Interfaces:
Serializable, Graph<V,E>
Direct Known Subclasses:
DirectedSubgraph, UndirectedSubgraph

public class Subgraph<V,E,G extends Graph<V,E>>
extends AbstractGraph<V,E>
implements Serializable
A subgraph is a graph that has a subset of vertices and a subset of edges with respect to some base graph. More formally, a subgraph G(V,E) that is based on a base graph Gb(Vb,Eb) satisfies the following subgraph property: V is a subset of Vb and E is a subset of Eb. Other than this property, a subgraph is a graph with any respect and fully complies with the Graph interface.

If the base graph is a ListenableGraph, the subgraph listens on the base graph and guarantees the subgraph property. If an edge or a vertex is removed from the base graph, it is automatically removed from the subgraph. Subgraph listeners are informed on such removal only if it results in a cascaded removal from the subgraph. If the subgraph has been created as an induced subgraph it also keeps track of edges being added to its vertices. If vertices are added to the base graph, the subgraph remains unaffected.

If the base graph is not a ListenableGraph, then the subgraph property cannot be guaranteed. If edges or vertices are removed from the base graph, they are not removed from the subgraph.

Modifications to Subgraph are allowed as long as the subgraph property is maintained. Addition of vertices or edges are allowed as long as they also exist in the base graph. Removal of vertices or edges is always allowed. The base graph is never affected by any modification made to the subgraph.

A subgraph may provide a "live-window" on a base graph, so that changes made to its vertices or edges are immediately reflected in the base graph, and vice versa. For that to happen, vertices and edges added to the subgraph must be identical (that is, reference-equal and not only value-equal) to their respective ones in the base graph. Previous versions of this class enforced such identity, at a severe performance cost. Currently it is no longer enforced. If you want to achieve a "live-window"functionality, your safest tactics would be to NOT override the equals() methods of your vertices and edges. If you use a class that has already overridden the equals() method, such as String, than you can use a wrapper around it, or else use it directly but exercise a great care to avoid having different-but-equal instances in the subgraph and the base graph.

This graph implementation guarantees deterministic vertex and edge set ordering (via LinkedHashSet).

Since:
Jul 18, 2003
Author:
Barak Naveh
Graph, Set, Serialized Form
• Constructor Summary

Constructors
Constructor and Description
Subgraph(G base, Set<V> vertexSubset)
Creates a new induced Subgraph.
Subgraph(G base, Set<V> vertexSubset, Set<E> edgeSubset)
Creates a new Subgraph.
• Method Summary

All Methods
Modifier and Type Method and Description
Creates a new edge in this graph, going from the source vertex to the target vertex, and returns the created edge.
boolean addEdge(V sourceVertex, V targetVertex, E e)
Adds the specified edge to this graph, going from the source vertex to the target vertex.
Adds the specified vertex to this subgraph.
boolean containsEdge(E e)
Returns true if this graph contains the specified edge.
boolean containsVertex(V v)
Returns true if this graph contains the specified vertex.
Set<E> edgeSet()
Returns a set of the edges contained in this graph.
Set<E> edgesOf(V vertex)
Returns a set of all edges touching the specified vertex.
Set<E> getAllEdges(V sourceVertex, V targetVertex)
Returns a set of all edges connecting source vertex to target vertex if such vertices exist in this graph.
G getBase()
Get the base graph.
E getEdge(V sourceVertex, V targetVertex)
Returns an edge connecting source vertex to target vertex if such vertices and such edge exist in this graph.
EdgeFactory<V,E> getEdgeFactory()
Returns the edge factory using which this graph creates new edges.
V getEdgeSource(E e)
Returns the source vertex of an edge.
V getEdgeTarget(E e)
Returns the target vertex of an edge.
double getEdgeWeight(E e)
Returns the weight assigned to a given edge.
boolean removeEdge(E e)
Removes the specified edge from the graph.
E removeEdge(V sourceVertex, V targetVertex)
Removes an edge going from source vertex to target vertex, if such vertices and such edge exist in this graph.
boolean removeVertex(V v)
Removes the specified vertex from this graph including all its touching edges if present.
void setEdgeWeight(E e, double weight)
Assigns a weight to an edge.
Set<V> vertexSet()
Returns a set of the vertices contained in this graph.
• Constructor Detail

• Subgraph

public Subgraph(G base,
Set<V> vertexSubset,
Set<E> edgeSubset)
Creates a new Subgraph.
Parameters:
base - the base (backing) graph on which the subgraph will be based.
vertexSubset - vertices to include in the subgraph. If null then all vertices are included.
edgeSubset - edges to in include in the subgraph. If null then all the edges whose vertices found in the graph are included.
• Subgraph

public Subgraph(G base,
Set<V> vertexSubset)
Creates a new induced Subgraph. The subgraph will keep track of edges being added to its vertex subset as well as deletion of edges and vertices. If base it not listenable, this is identical to the call Subgraph(base, vertexSubset, null) .
Parameters:
base - the base (backing) graph on which the subgraph will be based.
vertexSubset - vertices to include in the subgraph. If null then all vertices are included.
• Method Detail

• getAllEdges

public Set<E> getAllEdges(V sourceVertex,
V targetVertex)
Returns a set of all edges connecting source vertex to target vertex if such vertices exist in this graph. If any of the vertices does not exist or is null, returns null. If both vertices exist but no edges found, returns an empty set.

In undirected graphs, some of the returned edges may have their source and target vertices in the opposite order. In simple graphs the returned set is either singleton set or empty set.

Specified by:
getAllEdges in interface Graph<V,E>
Parameters:
sourceVertex - source vertex of the edge.
targetVertex - target vertex of the edge.
Returns:
a set of all edges connecting source vertex to target vertex.
• getEdge

public E getEdge(V sourceVertex,
V targetVertex)
Returns an edge connecting source vertex to target vertex if such vertices and such edge exist in this graph. Otherwise returns null. If any of the specified vertices is null returns null

In undirected graphs, the returned edge may have its source and target vertices in the opposite order.

Specified by:
getEdge in interface Graph<V,E>
Parameters:
sourceVertex - source vertex of the edge.
targetVertex - target vertex of the edge.
Returns:
an edge connecting source vertex to target vertex.
• getEdgeFactory

public EdgeFactory<V,E> getEdgeFactory()
Returns the edge factory using which this graph creates new edges. The edge factory is defined when the graph is constructed and must not be modified.
Specified by:
getEdgeFactory in interface Graph<V,E>
Returns:
the edge factory using which this graph creates new edges.

V targetVertex)
Creates a new edge in this graph, going from the source vertex to the target vertex, and returns the created edge. Some graphs do not allow edge-multiplicity. In such cases, if the graph already contains an edge from the specified source to the specified target, than this method does not change the graph and returns null.

The source and target vertices must already be contained in this graph. If they are not found in graph IllegalArgumentException is thrown.

This method creates the new edge e using this graph's EdgeFactory. For the new edge to be added e must not be equal to any other edge the graph (even if the graph allows edge-multiplicity). More formally, the graph must not contain any edge e2 such that e2.equals(e). If such e2 is found then the newly created edge e is abandoned, the method leaves this graph unchanged returns null.

Specified by:
Parameters:
sourceVertex - source vertex of the edge.
targetVertex - target vertex of the edge.
Returns:
The newly created edge if added to the graph, otherwise null.
Graph.getEdgeFactory()

V targetVertex,
E e)
Adds the specified edge to this graph, going from the source vertex to the target vertex. More formally, adds the specified edge, e, to this graph if this graph contains no edge e2 such that e2.equals(e). If this graph already contains such an edge, the call leaves this graph unchanged and returns false. Some graphs do not allow edge-multiplicity. In such cases, if the graph already contains an edge from the specified source to the specified target, than this method does not change the graph and returns false. If the edge was added to the graph, returns true.

The source and target vertices must already be contained in this graph. If they are not found in graph IllegalArgumentException is thrown.

Specified by:
Parameters:
sourceVertex - source vertex of the edge.
targetVertex - target vertex of the edge.
e - edge to be added to this graph.
Returns:
true if this graph did not already contain the specified edge.
• containsEdge

public boolean containsEdge(E e)
Returns true if this graph contains the specified edge. More formally, returns true if and only if this graph contains an edge e2 such that e.equals(e2). If the specified edge is null returns false.
Specified by:
containsEdge in interface Graph<V,E>
Parameters:
e - edge whose presence in this graph is to be tested.
Returns:
true if this graph contains the specified edge.
• containsVertex

public boolean containsVertex(V v)
Returns true if this graph contains the specified vertex. More formally, returns true if and only if this graph contains a vertex u such that u.equals(v). If the specified vertex is null returns false.
Specified by:
containsVertex in interface Graph<V,E>
Parameters:
v - vertex whose presence in this graph is to be tested.
Returns:
true if this graph contains the specified vertex.
• edgeSet

public Set<E> edgeSet()
Returns a set of the edges contained in this graph. The set is backed by the graph, so changes to the graph are reflected in the set. If the graph is modified while an iteration over the set is in progress, the results of the iteration are undefined.

The graph implementation may maintain a particular set ordering (e.g. via LinkedHashSet) for deterministic iteration, but this is not required. It is the responsibility of callers who rely on this behavior to only use graph implementations which support it.

Specified by:
edgeSet in interface Graph<V,E>
Returns:
a set of the edges contained in this graph.
• edgesOf

public Set<E> edgesOf(V vertex)
Returns a set of all edges touching the specified vertex. If no edges are touching the specified vertex returns an empty set.
Specified by:
edgesOf in interface Graph<V,E>
Parameters:
vertex - the vertex for which a set of touching edges is to be returned.
Returns:
a set of all edges touching the specified vertex.
• removeEdge

public boolean removeEdge(E e)
Removes the specified edge from the graph. Removes the specified edge from this graph if it is present. More formally, removes an edge e2 such that e2.equals(e), if the graph contains such edge. Returns true if the graph contained the specified edge. (The graph will not contain the specified edge once the call returns).

If the specified edge is null returns false.

Specified by:
removeEdge in interface Graph<V,E>
Parameters:
e - edge to be removed from this graph, if present.
Returns:
true if and only if the graph contained the specified edge.
• removeEdge

public E removeEdge(V sourceVertex,
V targetVertex)
Removes an edge going from source vertex to target vertex, if such vertices and such edge exist in this graph. Returns the edge if removed or null otherwise.
Specified by:
removeEdge in interface Graph<V,E>
Parameters:
sourceVertex - source vertex of the edge.
targetVertex - target vertex of the edge.
Returns:
The removed edge, or null if no edge removed.
• removeVertex

public boolean removeVertex(V v)
Removes the specified vertex from this graph including all its touching edges if present. More formally, if the graph contains a vertex u such that u.equals(v), the call removes all edges that touch u and then removes u itself. If no such u is found, the call leaves the graph unchanged. Returns true if the graph contained the specified vertex. (The graph will not contain the specified vertex once the call returns).

If the specified vertex is null returns false.

Specified by:
removeVertex in interface Graph<V,E>
Parameters:
v - vertex to be removed from this graph, if present.
Returns:
true if the graph contained the specified vertex; false otherwise.
• vertexSet

public Set<V> vertexSet()
Returns a set of the vertices contained in this graph. The set is backed by the graph, so changes to the graph are reflected in the set. If the graph is modified while an iteration over the set is in progress, the results of the iteration are undefined.

The graph implementation may maintain a particular set ordering (e.g. via LinkedHashSet) for deterministic iteration, but this is not required. It is the responsibility of callers who rely on this behavior to only use graph implementations which support it.

Specified by:
vertexSet in interface Graph<V,E>
Returns:
a set view of the vertices contained in this graph.
• getEdgeSource

public V getEdgeSource(E e)
Returns the source vertex of an edge. For an undirected graph, source and target are distinguishable designations (but without any mathematical meaning).
Specified by:
getEdgeSource in interface Graph<V,E>
Parameters:
e - edge of interest
Returns:
source vertex
• getEdgeTarget

public V getEdgeTarget(E e)
Returns the target vertex of an edge. For an undirected graph, source and target are distinguishable designations (but without any mathematical meaning).
Specified by:
getEdgeTarget in interface Graph<V,E>
Parameters:
e - edge of interest
Returns:
target vertex
• getBase

public G getBase()
Get the base graph.
Returns:
the base graph
• getEdgeWeight

public double getEdgeWeight(E e)
Returns the weight assigned to a given edge. Unweighted graphs return 1.0 (as defined by WeightedGraph.DEFAULT_EDGE_WEIGHT), allowing weighted-graph algorithms to apply to them where meaningful.
Specified by:
getEdgeWeight in interface Graph<V,E>
Parameters:
e - edge of interest
Returns:
edge weight