Interface Graph<N>

 Type Parameters:
N
 Node parameter type
 All Superinterfaces:
PredecessorsFunction<N>
,SuccessorsFunction<N>
 All Known Subinterfaces:
MutableGraph<N>
 All Known Implementing Classes:
AbstractGraph
,ImmutableGraph
@Beta @DoNotMock("Use GraphBuilder to create a real instance") public interface Graph<N>
An interface for graphstructured data, whose edges are anonymous entities with no identity or information of their own.A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
There are three primary interfaces provided to represent graphs. In order of increasing complexity they are:
Graph
,ValueGraph
, andNetwork
. You should generally prefer the simplest interface that satisfies your use case. See the "Choosing the right graph type" section of the Guava User Guide for more details.Capabilities
Graph
supports the following use cases (definitions of terms): directed graphs
 undirected graphs
 graphs that do/don't allow selfloops
 graphs whose nodes/edges are insertionordered, sorted, or unordered
Graph
explicitly does not support parallel edges, and forbids implementations or extensions with parallel edges. If you need parallel edges, useNetwork
.Building a
Graph
The implementation classes that
common.graph
provides are not public, by design. To create an instance of one of the builtin implementations ofGraph
, use theGraphBuilder
class:MutableGraph<Integer> graph = GraphBuilder.undirected().build();
GraphBuilder.build()
returns an instance ofMutableGraph
, which is a subtype ofGraph
that provides methods for adding and removing nodes and edges. If you do not need to mutate a graph (e.g. if you write a method than runs a readonly algorithm on the graph), you should use the nonmutatingGraph
interface, or anImmutableGraph
.You can create an immutable copy of an existing
Graph
usingImmutableGraph.copyOf(Graph)
:ImmutableGraph<Integer> immutableGraph = ImmutableGraph.copyOf(graph);
Instances of
ImmutableGraph
do not implementMutableGraph
(obviously!) and are contractually guaranteed to be unmodifiable and threadsafe.The Guava User Guide has more information on (and examples of) building graphs.
Additional documentation
See the Guava User Guide for the
common.graph
package ("Graphs Explained") for additional documentation, including: Since:
 20.0
 Author:
 James Sexton, Joshua O'Madadhain


Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description Set<N>
adjacentNodes(N node)
Returns the nodes which have an incident edge in common withnode
in this graph.boolean
allowsSelfLoops()
Returns true if this graph allows selfloops (edges that connect a node to itself).int
degree(N node)
Returns the count ofnode
's incident edges, counting selfloops twice (equivalently, the number of times an edge touchesnode
).Set<EndpointPair<N>>
edges()
Returns all edges in this graph.boolean
equals(Object object)
Returnstrue
iffobject
is aGraph
that has the same elements and the same structural relationships as those in this graph.boolean
hasEdgeConnecting(EndpointPair<N> endpoints)
Returns true if there is an edge that directly connectsendpoints
(in the order, if any, specified byendpoints
).boolean
hasEdgeConnecting(N nodeU, N nodeV)
Returns true if there is an edge that directly connectsnodeU
tonodeV
.int
hashCode()
Returns the hash code for this graph.ElementOrder<N>
incidentEdgeOrder()
Returns anElementOrder
that specifies the order of iteration for the elements ofedges()
,adjacentNodes(Object)
,predecessors(Object)
,successors(Object)
andincidentEdges(Object)
.Set<EndpointPair<N>>
incidentEdges(N node)
Returns the edges in this graph whose endpoints includenode
.int
inDegree(N node)
Returns the count ofnode
's incoming edges (equal topredecessors(node).size()
) in a directed graph.boolean
isDirected()
Returns true if the edges in this graph are directed.ElementOrder<N>
nodeOrder()
Returns the order of iteration for the elements ofnodes()
.Set<N>
nodes()
Returns all nodes in this graph, in the order specified bynodeOrder()
.int
outDegree(N node)
Returns the count ofnode
's outgoing edges (equal tosuccessors(node).size()
) in a directed graph.Set<N>
predecessors(N node)
Returns all nodes in this graph adjacent tonode
which can be reached by traversingnode
's incoming edges against the direction (if any) of the edge.Set<N>
successors(N node)
Returns all nodes in this graph adjacent tonode
which can be reached by traversingnode
's outgoing edges in the direction (if any) of the edge.



Method Detail

nodes
Set<N> nodes()
Returns all nodes in this graph, in the order specified bynodeOrder()
.

edges
Set<EndpointPair<N>> edges()
Returns all edges in this graph.

isDirected
boolean isDirected()
Returns true if the edges in this graph are directed. Directed edges connect asource node
to atarget node
, while undirected edges connect a pair of nodes to each other.

allowsSelfLoops
boolean allowsSelfLoops()
Returns true if this graph allows selfloops (edges that connect a node to itself). Attempting to add a selfloop to a graph that does not allow them will throw anIllegalArgumentException
.

nodeOrder
ElementOrder<N> nodeOrder()
Returns the order of iteration for the elements ofnodes()
.

incidentEdgeOrder
ElementOrder<N> incidentEdgeOrder()
Returns anElementOrder
that specifies the order of iteration for the elements ofedges()
,adjacentNodes(Object)
,predecessors(Object)
,successors(Object)
andincidentEdges(Object)
. Since:
 29.0

adjacentNodes
Set<N> adjacentNodes(N node)
Returns the nodes which have an incident edge in common withnode
in this graph.This is equal to the union of
predecessors(Object)
andsuccessors(Object)
. Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

predecessors
Set<N> predecessors(N node)
Returns all nodes in this graph adjacent tonode
which can be reached by traversingnode
's incoming edges against the direction (if any) of the edge.In an undirected graph, this is equivalent to
adjacentNodes(Object)
. Specified by:
predecessors
in interfacePredecessorsFunction<N>
 Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

successors
Set<N> successors(N node)
Returns all nodes in this graph adjacent tonode
which can be reached by traversingnode
's outgoing edges in the direction (if any) of the edge.In an undirected graph, this is equivalent to
adjacentNodes(Object)
.This is not the same as "all nodes reachable from
node
by following outgoing edges". For that functionality, seeGraphs.reachableNodes(Graph, Object)
. Specified by:
successors
in interfaceSuccessorsFunction<N>
 Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

incidentEdges
Set<EndpointPair<N>> incidentEdges(N node)
Returns the edges in this graph whose endpoints includenode
.This is equal to the union of incoming and outgoing edges.
 Throws:
IllegalArgumentException
 ifnode
is not an element of this graph Since:
 24.0

degree
int degree(N node)
Returns the count ofnode
's incident edges, counting selfloops twice (equivalently, the number of times an edge touchesnode
).For directed graphs, this is equal to
inDegree(node) + outDegree(node)
.For undirected graphs, this is equal to
incidentEdges(node).size()
+ (number of selfloops incident tonode
).If the count is greater than
Integer.MAX_VALUE
, returnsInteger.MAX_VALUE
. Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

inDegree
int inDegree(N node)
Returns the count ofnode
's incoming edges (equal topredecessors(node).size()
) in a directed graph. In an undirected graph, returns thedegree(Object)
.If the count is greater than
Integer.MAX_VALUE
, returnsInteger.MAX_VALUE
. Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

outDegree
int outDegree(N node)
Returns the count ofnode
's outgoing edges (equal tosuccessors(node).size()
) in a directed graph. In an undirected graph, returns thedegree(Object)
.If the count is greater than
Integer.MAX_VALUE
, returnsInteger.MAX_VALUE
. Throws:
IllegalArgumentException
 ifnode
is not an element of this graph

hasEdgeConnecting
boolean hasEdgeConnecting(N nodeU, N nodeV)
Returns true if there is an edge that directly connectsnodeU
tonodeV
. This is equivalent tonodes().contains(nodeU) && successors(nodeU).contains(nodeV)
.In an undirected graph, this is equal to
hasEdgeConnecting(nodeV, nodeU)
. Since:
 23.0

hasEdgeConnecting
boolean hasEdgeConnecting(EndpointPair<N> endpoints)
Returns true if there is an edge that directly connectsendpoints
(in the order, if any, specified byendpoints
). This is equivalent toedges().contains(endpoints)
.Unlike the other
EndpointPair
accepting methods, this method does not throw if the endpoints are unordered and the graph is directed; it simply returnsfalse
. This is for consistency with the behavior ofCollection.contains(Object)
(which does not generally throw if the object cannot be present in the collection), and the desire to have this method's behavior be compatible withedges().contains(endpoints)
. Since:
 27.1

equals
boolean equals(@CheckForNull Object object)
Returnstrue
iffobject
is aGraph
that has the same elements and the same structural relationships as those in this graph.Thus, two graphs A and B are equal if all of the following are true:
 A and B have equal
directedness
.  A and B have equal
node sets
.  A and B have equal
edge sets
.
Graph properties besides
directedness
do not affect equality. For example, two graphs may be considered equal even if one allows selfloops and the other doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order in which they are iterated over, are irrelevant.A reference implementation of this is provided by
AbstractGraph.equals(Object)
. Overrides:
equals
in classObject
 Parameters:
object
 the reference object with which to compare. Returns:
true
if this object is the same as the obj argument;false
otherwise. See Also:
Object.hashCode()
,HashMap
 A and B have equal

hashCode
int hashCode()
Returns the hash code for this graph. The hash code of a graph is defined as the hash code of the set returned byedges()
.A reference implementation of this is provided by
AbstractGraph.hashCode()
. Overrides:
hashCode
in classObject
 Returns:
 a hash code value for this object.
 See Also:
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)

