N
 Node parameter type@Beta @DoNotMock(value="Use GraphBuilder to create a real instance") public interface Graph<N>
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
, and Network
. 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.
Graph
supports the following use cases (definitions of
terms):
Graph
explicitly does not support parallel edges, and forbids implementations or
extensions with parallel edges. If you need parallel edges, use Network
.
Graph
The implementation classes that common.graph
provides are not public, by design. To
create an instance of one of the builtin implementations of Graph
, use the GraphBuilder
class:
MutableGraph<Integer> graph = GraphBuilder.undirected().build();
GraphBuilder.build()
returns an instance of MutableGraph
, which is a subtype
of Graph
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 nonmutating Graph
interface, or an ImmutableGraph
.
You can create an immutable copy of an existing Graph
using ImmutableGraph.copyOf(Graph)
:
ImmutableGraph<Integer> immutableGraph = ImmutableGraph.copyOf(graph);
Instances of ImmutableGraph
do not implement MutableGraph
(obviously!) and are
contractually guaranteed to be unmodifiable and threadsafe.
The Guava User Guide has more information on (and examples of) building graphs.
See the Guava User Guide for the common.graph
package ("Graphs Explained") for
additional documentation, including:
Modifier and Type  Method and Description 

Set<N> 
adjacentNodes(N node)
Returns the nodes which have an incident edge in common with
node 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 of
node 's incident edges, counting selfloops twice (equivalently,
the number of times an edge touches node ). 
Set<EndpointPair<N>> 
edges()
Returns all edges in this graph.

boolean 
equals(@Nullable Object object)
Returns
true iff object is a Graph 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 connects
endpoints (in the order, if
any, specified by endpoints ). 
boolean 
hasEdgeConnecting(N nodeU,
N nodeV)
Returns true if there is an edge that directly connects
nodeU to nodeV . 
int 
hashCode()
Returns the hash code for this graph.

Set<EndpointPair<N>> 
incidentEdges(N node)
Returns the edges in this graph whose endpoints include
node . 
int 
inDegree(N node)
Returns the count of
node 's incoming edges (equal to predecessors(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 of
nodes() . 
Set<N> 
nodes()
Returns all nodes in this graph, in the order specified by
nodeOrder() . 
int 
outDegree(N node)
Returns the count of
node 's outgoing edges (equal to successors(node).size() )
in a directed graph. 
Set<N> 
predecessors(N node)
Returns all nodes in this graph adjacent to
node which can be reached by traversing
node 's incoming edges against the direction (if any) of the edge. 
Set<N> 
successors(N node)
Returns all nodes in this graph adjacent to
node which can be reached by traversing
node 's outgoing edges in the direction (if any) of the edge. 
Set<N> nodes()
nodeOrder()
.Set<EndpointPair<N>> edges()
boolean isDirected()
source node
to a target node
, while
undirected edges connect a pair of nodes to each other.boolean allowsSelfLoops()
IllegalArgumentException
.ElementOrder<N> nodeOrder()
nodes()
.Set<N> adjacentNodes(N node)
node
in this graph.
This is equal to the union of predecessors(Object)
and successors(Object)
.
IllegalArgumentException
 if node
is not an element of this graphSet<N> predecessors(N node)
node
which can be reached by traversing
node
's incoming edges against the direction (if any) of the edge.
In an undirected graph, this is equivalent to adjacentNodes(Object)
.
IllegalArgumentException
 if node
is not an element of this graphSet<N> successors(N node)
node
which can be reached by traversing
node
'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, see Graphs.reachableNodes(Graph, Object)
.
IllegalArgumentException
 if node
is not an element of this graphSet<EndpointPair<N>> incidentEdges(N node)
node
.
This is equal to the union of incoming and outgoing edges.
IllegalArgumentException
 if node
is not an element of this graphint degree(N node)
node
's incident edges, counting selfloops twice (equivalently,
the number of times an edge touches node
).
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 to node
).
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
IllegalArgumentException
 if node
is not an element of this graphint inDegree(N node)
node
's incoming edges (equal to predecessors(node).size()
)
in a directed graph. In an undirected graph, returns the degree(Object)
.
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
IllegalArgumentException
 if node
is not an element of this graphint outDegree(N node)
node
's outgoing edges (equal to successors(node).size()
)
in a directed graph. In an undirected graph, returns the degree(Object)
.
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
IllegalArgumentException
 if node
is not an element of this graphboolean hasEdgeConnecting(N nodeU, N nodeV)
nodeU
to nodeV
. This is
equivalent to nodes().contains(nodeU) && successors(nodeU).contains(nodeV)
.
In an undirected graph, this is equal to hasEdgeConnecting(nodeV, nodeU)
.
boolean hasEdgeConnecting(EndpointPair<N> endpoints)
endpoints
(in the order, if
any, specified by endpoints
). This is equivalent to edges().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 returns false
. This is for
consistency with the behavior of Collection.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 with edges().contains(endpoints)
.
boolean equals(@Nullable Object object)
true
iff object
is a Graph
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:
directedness
.
node sets
.
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)
.
equals
in class Object
object
 the reference object with which to compare.true
if this object is the same as the obj
argument; false
otherwise.Object.hashCode()
,
HashMap
int hashCode()
edges()
.
A reference implementation of this is provided by AbstractGraph.hashCode()
.
hashCode
in class Object
Object.equals(java.lang.Object)
,
System.identityHashCode(java.lang.Object)
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