## Class AsSubgraph<V,​E>

• Type Parameters:
V - the vertex type
E - the edge type
All Implemented Interfaces:
java.io.Serializable, Graph<V,​E>

public class AsSubgraph<V,​E>
extends AbstractGraph<V,​E>
implements java.io.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, then 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).

Note that this implementation tries to maintain a "live-window" 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.

Author:
Barak Naveh
Graph, Set, Serialized Form
• ### Field Summary

Fields
Modifier and Type Field Description
protected Graph<V,​E> base
protected GraphType baseType
protected java.util.Set<E> edgeSet
protected boolean isInduced
protected java.util.Set<V> vertexSet
• ### Fields inherited from interface org.jgrapht.Graph

DEFAULT_EDGE_WEIGHT
• ### Constructor Summary

Constructors
Constructor Description
AsSubgraph​(Graph<V,​E> base)
Creates a new induced Subgraph with all vertices included.
AsSubgraph​(Graph<V,​E> base, java.util.Set<? extends V> vertexSubset)
Creates a new induced subgraph.
AsSubgraph​(Graph<V,​E> base, java.util.Set<? extends V> vertexSubset, java.util.Set<? extends E> edgeSubset)
Creates a new subgraph.
• ### Method Summary

All Methods
Modifier and Type Method 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.
V addVertex()
Creates a new vertex in this graph and returns it.
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.
int degreeOf​(V vertex)
Returns the degree of the specified vertex.
java.util.Set<E> edgeSet()
Returns a set of the edges contained in this graph.
java.util.Set<E> edgesOf​(V vertex)
Returns a set of all edges touching the specified vertex.
java.util.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.
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.
V getEdgeSource​(E e)
Returns the source vertex of an edge.
java.util.function.Supplier<E> getEdgeSupplier()
Return the edge supplier that the graph uses whenever it needs to create new edges.
V getEdgeTarget​(E e)
Returns the target vertex of an edge.
double getEdgeWeight​(E e)
Returns the weight assigned to a given edge.
GraphType getType()
Get the graph type.
java.util.function.Supplier<V> getVertexSupplier()
Return the vertex supplier that the graph uses whenever it needs to create new vertices.
java.util.Set<E> incomingEdgesOf​(V vertex)
Returns a set of all edges incoming into the specified vertex.
int inDegreeOf​(V vertex)
Returns the "in degree" of the specified vertex.
int outDegreeOf​(V vertex)
Returns the "out degree" of the specified vertex.
java.util.Set<E> outgoingEdgesOf​(V vertex)
Returns a set of all edges outgoing from the specified vertex.
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.
java.util.Set<V> vertexSet()
Returns a set of the vertices contained in this graph.
• ### Methods inherited from class org.jgrapht.graph.AbstractGraph

assertVertexExist, containsEdge, equals, hashCode, removeAllEdges, removeAllEdges, removeAllEdges, removeAllVertices, toString, toStringFromSets
• ### Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait
• ### Methods inherited from interface org.jgrapht.Graph

iterables, setEdgeWeight
• ### Field Detail

• #### edgeSet

protected final java.util.Set<E> edgeSet
• #### vertexSet

protected final java.util.Set<V> vertexSet
• #### base

protected final Graph<V,​E> base
• #### baseType

protected final GraphType baseType
• #### isInduced

protected final boolean isInduced
• ### Constructor Detail

• #### AsSubgraph

public AsSubgraph​(Graph<V,​E> base,
java.util.Set<? extends V> vertexSubset,
java.util.Set<? extends 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.
• #### AsSubgraph

public AsSubgraph​(Graph<V,​E> base,
java.util.Set<? extends 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.
• #### AsSubgraph

public AsSubgraph​(Graph<V,​E> base)
Creates a new induced Subgraph with all vertices included. The subgraph will keep track of edges being added to its vertex subset as well as deletion of edges and vertices. If base is not listenable, this is identical to the call Subgraph(base, null, null).
Parameters:
base - the base (backing) graph on which the subgraph will be based.
• ### Method Detail

• #### getAllEdges

public java.util.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.
• #### getVertexSupplier

public java.util.function.Supplier<V> getVertexSupplier()
Return the vertex supplier that the graph uses whenever it needs to create new vertices.

A graph uses the vertex supplier to create new vertex objects whenever a user calls method Graph.addVertex(). Users can also create the vertex in user code and then use method Graph.addVertex(Object) to add the vertex.

In contrast with the Supplier interface, the vertex supplier has the additional requirement that a new and distinct result is returned every time it is invoked. More specifically for a new vertex to be added in a graph v must not be equal to any other vertex in the graph. More formally, the graph must not contain any vertex v2 such that v2.equals(v).

Care must also be taken when interchanging calls to methods Graph.addVertex(Object) and Graph.addVertex(). In such a case the user must make sure never to add vertices in the graph using method Graph.addVertex(Object), which are going to be returned in the future by the supplied vertex supplier. Such a sequence will result into an IllegalArgumentException when calling method Graph.addVertex().

Specified by:
getVertexSupplier in interface Graph<V,​E>
Returns:
the vertex supplier or null if the graph has no such supplier
• #### getEdgeSupplier

public java.util.function.Supplier<E> getEdgeSupplier()
Return the edge supplier that the graph uses whenever it needs to create new edges.

A graph uses the edge supplier to create new edge objects whenever a user calls method Graph.addEdge(Object, Object). Users can also create the edge in user code and then use method Graph.addEdge(Object, Object, Object) to add the edge.

In contrast with the Supplier interface, the edge supplier has the additional requirement that a new and distinct result is returned every time it is invoked. More specifically for a new edge to be added in a graph e must not be equal to any other edge in the graph (even if the graph allows edge-multiplicity). More formally, the graph must not contain any edge e2 such that e2.equals(e).

Specified by:
getEdgeSupplier in interface Graph<V,​E>
Returns:
the edge supplier null if the graph has no such supplier

public E addEdge​(V sourceVertex,
V targetVertex)
Add an edge to the subgraph. The end-points must exist in the subgraph and the edge must exist in the base graph. In case multiple such edges exist in the base graph, one that is not already in the subgraph is chosen arbitrarily and added to the subgraph. In case all such edges already exist in the subgraph, the method returns null.
Specified by:
addEdge in interface Graph<V,​E>
Parameters:
sourceVertex - the source vertex
targetVertex - the source vertex
Returns:
the added edge or null if all such edges from the base graph already belong in the subgraph
Throws:
java.lang.IllegalArgumentException - if the source or target vertex does not belong to the subgraph
java.lang.IllegalArgumentException - if the base graph does not contain any edge between the two end-points
Graph.getEdgeSupplier()

public boolean addEdge​(V sourceVertex,
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, then 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:
addEdge in interface Graph<V,​E>
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.
Graph.addEdge(Object, Object), Graph.getEdgeSupplier()

public V addVertex()
Description copied from interface: Graph
Creates a new vertex in this graph and returns it.

This method creates the new vertex v using this graph's vertex supplier (see Graph.getVertexSupplier()). For the new vertex to be added v must not be equal to any other vertex in the graph. More formally, the graph must not contain any vertex v2 such that v2.equals(v). If such  v2 is found then the newly created vertex v is abandoned, the method leaves this graph unchanged and throws an IllegalArgumentException.

If the underlying graph implementation's Graph.getVertexSupplier() returns null, then this method cannot create vertices and throws an UnsupportedOperationException.

Care must also be taken when interchanging calls to methods Graph.addVertex(Object) and Graph.addVertex(). In such a case the user must make sure never to add vertices in the graph using method Graph.addVertex(Object), which are going to be returned in the future by the supplied vertex supplier. Such a sequence will result into an IllegalArgumentException when calling method Graph.addVertex().

Specified by:
addVertex in interface Graph<V,​E>
Returns:
The newly created vertex if added to the graph.
Graph.getVertexSupplier()

public boolean addVertex​(V v)
Adds the specified vertex to this subgraph.
Specified by:
addVertex in interface Graph<V,​E>
Parameters:
v - the vertex to be added.
Returns:
true if the vertex was added, otherwise  false.
Throws:
java.lang.NullPointerException - if v is null
java.lang.IllegalArgumentException - if the base graph does not contain the vertex
AsSubgraph, Graph.addVertex(Object)
• #### 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 java.util.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 java.util.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.
• #### degreeOf

public int degreeOf​(V vertex)
Returns the degree of the specified vertex.

A degree of a vertex in an undirected graph is the number of edges touching that vertex. Edges with same source and target vertices (self-loops) are counted twice.

In directed graphs this method returns the sum of the "in degree" and the "out degree".

By default this method returns the sum of in-degree and out-degree. The exact value returned depends on the types of the underlying graph.

Specified by:
degreeOf in interface Graph<V,​E>
Parameters:
vertex - vertex whose degree is to be calculated.
Returns:
the degree of the specified vertex.
• #### incomingEdgesOf

public java.util.Set<E> incomingEdgesOf​(V vertex)
Returns a set of all edges incoming into the specified vertex.

In the case of undirected graphs this method returns all edges touching the vertex, thus, some of the returned edges may have their source and target vertices in the opposite order.

Specified by:
incomingEdgesOf in interface Graph<V,​E>
Parameters:
vertex - the vertex for which the list of incoming edges to be returned.
Returns:
a set of all edges incoming into the specified vertex.
• #### inDegreeOf

public int inDegreeOf​(V vertex)
Returns the "in degree" of the specified vertex.

The "in degree" of a vertex in a directed graph is the number of inward directed edges from that vertex. See http://mathworld.wolfram.com/Indegree.html.

In the case of undirected graphs this method returns the number of edges touching the vertex. Edges with same source and target vertices (self-loops) are counted twice.

Specified by:
inDegreeOf in interface Graph<V,​E>
Parameters:
vertex - vertex whose degree is to be calculated.
Returns:
the degree of the specified vertex.
• #### outgoingEdgesOf

public java.util.Set<E> outgoingEdgesOf​(V vertex)
Returns a set of all edges outgoing from the specified vertex.

In the case of undirected graphs this method returns all edges touching the vertex, thus, some of the returned edges may have their source and target vertices in the opposite order.

Specified by:
outgoingEdgesOf in interface Graph<V,​E>
Parameters:
vertex - the vertex for which the list of outgoing edges to be returned.
Returns:
a set of all edges outgoing from the specified vertex.
• #### outDegreeOf

public int outDegreeOf​(V vertex)
Returns the "out degree" of the specified vertex.

The "out degree" of a vertex in a directed graph is the number of outward directed edges from that vertex. See http://mathworld.wolfram.com/Outdegree.html.

In the case of undirected graphs this method returns the number of edges touching the vertex. Edges with same source and target vertices (self-loops) are counted twice.

Specified by:
outDegreeOf in interface Graph<V,​E>
Parameters:
vertex - vertex whose degree is to be calculated.
Returns:
the degree of 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 java.util.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
• #### getType

public GraphType getType()
Get the graph type. The graph type can be used to query for additional metadata such as whether the graph supports directed or undirected edges, self-loops, multiple (parallel) edges, weights, etc.
Specified by:
getType in interface Graph<V,​E>
Returns:
the graph type
• #### getEdgeWeight

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

public void setEdgeWeight​(E e,
double weight)
Assigns a weight to an edge.
Specified by:
setEdgeWeight in interface Graph<V,​E>
Parameters:
e - edge on which to set weight
weight - new weight for edge