V
 the vertex typeE
 the edge typeG
 the type of the base graphpublic class Subgraph<V,E,G extends Graph<V,E>> extends AbstractGraph<V,E> implements Serializable
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 "livewindow" 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, referenceequal and not only
valueequal) 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 "livewindow" 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
differentbutequal instances in the subgraph and the base graph.
This graph implementation guarantees deterministic vertex and edge set ordering (via
LinkedHashSet
).
Note that this implementation tries to maintain a "livewindow" on the base graph, which has implications in the performance of the various operations. For example iterating over the adjacent edges of a vertex takes time proportional to the number of adjacent edges of the vertex in the base graph even if the subgraph contains only a small subset of those edges. Therefore, the user must be aware that using this implementation for certain algorithms might come with computational overhead. For certain algorithms it is better to maintain a subgraph by hand instead of using this implementation as a black box.
Graph
,
Set
,
Serialized FormModifier and Type  Field and Description 

protected G 
base 
protected Set<E> 
edgeSet 
protected boolean 
isInduced 
protected Set<V> 
vertexSet 
Constructor and Description 

Subgraph(G base)
Creates a new induced Subgraph with all vertices included.

Subgraph(G base,
Set<? extends V> vertexSubset)
Creates a new induced Subgraph.

Subgraph(G base,
Set<? extends V> vertexSubset,
Set<? extends E> edgeSubset)
Creates a new Subgraph.

Modifier and Type  Method and Description 

E 
addEdge(V sourceVertex,
V targetVertex)
Add an edge to the subgraph.

boolean 
addEdge(V sourceVertex,
V targetVertex,
E e)
Adds the specified edge to this graph, going from the source vertex to the target vertex.

boolean 
addVertex(V v)
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.

assertVertexExist, containsEdge, equals, hashCode, removeAllEdges, removeAllEdges, removeAllEdges, removeAllVertices, toString, toStringFromSets
public Subgraph(G base, Set<? extends V> vertexSubset, Set<? extends E> edgeSubset)
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.public Subgraph(G base, Set<? extends V> vertexSubset)
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.public Subgraph(G base)
base
 the base (backing) graph on which the subgraph will be based.public Set<E> getAllEdges(V sourceVertex, V targetVertex)
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.
getAllEdges
in interface Graph<V,E>
sourceVertex
 source vertex of the edge.targetVertex
 target vertex of the edge.public E getEdge(V sourceVertex, V targetVertex)
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.
public EdgeFactory<V,E> getEdgeFactory()
getEdgeFactory
in interface Graph<V,E>
public E addEdge(V sourceVertex, V targetVertex)
addEdge
in interface Graph<V,E>
sourceVertex
 the source vertextargetVertex
 the source vertexIllegalArgumentException
 if the source or target vertex does not belong to the
subgraphIllegalArgumentException
 if the base graph does not contain any edge between the two
endpointsGraph.getEdgeFactory()
public boolean addEdge(V sourceVertex, V targetVertex, E e)
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 edgemultiplicity. 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.
addEdge
in interface Graph<V,E>
sourceVertex
 source vertex of the edge.targetVertex
 target vertex of the edge.e
 edge to be added to this graph.Graph.addEdge(Object, Object)
,
Graph.getEdgeFactory()
public boolean addVertex(V v)
addVertex
in interface Graph<V,E>
v
 the vertex to be added.true
if the vertex was added, otherwise
false
.NullPointerException
 if v is nullIllegalArgumentException
 if the base graph does not contain the vertexSubgraph
,
Graph.addVertex(Object)
public boolean containsEdge(E e)
e2
such that
e.equals(e2)
. If the specified edge is null
returns
false
.containsEdge
in interface Graph<V,E>
e
 edge whose presence in this graph is to be tested.public boolean containsVertex(V v)
u
such that
u.equals(v)
. If the specified vertex is null
returns
false
.containsVertex
in interface Graph<V,E>
v
 vertex whose presence in this graph is to be tested.public Set<E> edgeSet()
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.
public Set<E> edgesOf(V vertex)
public boolean removeEdge(E e)
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
.
removeEdge
in interface Graph<V,E>
e
 edge to be removed from this graph, if present.true
if and only if the graph contained the specified edge.public E removeEdge(V sourceVertex, V targetVertex)
null
otherwise.removeEdge
in interface Graph<V,E>
sourceVertex
 source vertex of the edge.targetVertex
 target vertex of the edge.null
if no edge removed.public boolean removeVertex(V v)
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
.
removeVertex
in interface Graph<V,E>
v
 vertex to be removed from this graph, if present.true
if the graph contained the specified vertex; false
otherwise.public Set<V> vertexSet()
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.
public V getEdgeSource(E e)
getEdgeSource
in interface Graph<V,E>
e
 edge of interestpublic V getEdgeTarget(E e)
getEdgeTarget
in interface Graph<V,E>
e
 edge of interestpublic G getBase()
public double getEdgeWeight(E e)
WeightedGraph.DEFAULT_EDGE_WEIGHT
), allowing weightedgraph algorithms to apply to
them where meaningful.getEdgeWeight
in interface Graph<V,E>
e
 edge of interestWeightedGraph
public void setEdgeWeight(E e, double weight)
e
 edge on which to set weightweight
 new weight for edgeWeightedGraph.setEdgeWeight(Object, double)
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