com.google.common.graph

Interface ValueGraph<N,V>

Type Parameters:

N - Node parameter type

V - Value parameter type

All Known Subinterfaces:

MutableValueGraph<N,V>

All Known Implementing Classes:

AbstractValueGraph, ImmutableValueGraph

@Beta
public interface ValueGraph<N,V>

An interface for graph-structured data, whose edges have associated non-unique values.

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.

Capabilities

ValueGraph supports the following use cases (definitions of terms):

• directed graphs
• undirected graphs
• graphs that do/don't allow self-loops
• graphs whose nodes/edges are insertion-ordered, sorted, or unordered
• graphs whose edges have associated values

ValueGraph, as a subtype of Graph, explicitly does not support parallel edges, and forbids implementations or extensions with parallel edges. If you need parallel edges, use Network. (You can use a positive Integer edge value as a loose representation of edge multiplicity, but the *degree() and mutation methods will not reflect your interpretation of the edge value as its multiplicity.)

Building a ValueGraph

The implementation classes that common.graph provides are not public, by design. To create an instance of one of the built-in implementations of ValueGraph, use the ValueGraphBuilder class:

 MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build();
 

ValueGraphBuilder.build() returns an instance of MutableValueGraph, which is a subtype of ValueGraph 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 read-only algorithm on the graph), you should use the non-mutating ValueGraph interface, or an ImmutableValueGraph.

You can create an immutable copy of an existing ValueGraph using ImmutableValueGraph.copyOf(ValueGraph):

 ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph);
 

Instances of ImmutableValueGraph do not implement MutableValueGraph (obviously!) and are contractually guaranteed to be unmodifiable and thread-safe.

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:

• equals(), hashCode(), and graph equivalence
• Synchronization policy
• Notes for implementors

Since:

20.0

Author:

James Sexton, Joshua O'Madadhain

Method Summary

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 self-loops (edges that connect a node to itself).
Graph<N>	asGraph() Returns a live view of this graph as a Graph.
int	degree(N node) Returns the count of node's incident edges, counting self-loops twice (equivalently, the number of times an edge touches node).
Set<EndpointPair<N>>	edges() Returns all edges in this graph.
Optional<V>	edgeValue(EndpointPair<N> endpoints) Returns the value of the edge that connects endpoints (in the order, if any, specified by endpoints), if one is present; otherwise, returns Optional.empty().
Optional<V>	edgeValue(N nodeU, N nodeV) Returns the value of the edge that connects nodeU to nodeV (in the order, if any, specified by endpoints), if one is present; otherwise, returns Optional.empty().
V	edgeValueOrDefault(EndpointPair<N> endpoints, V defaultValue) Returns the value of the edge that connects endpoints (in the order, if any, specified by endpoints), if one is present; otherwise, returns defaultValue.
V	edgeValueOrDefault(N nodeU, N nodeV, V defaultValue) Returns the value of the edge that connects nodeU to nodeV, if one is present; otherwise, returns defaultValue.
boolean	equals(@Nullable Object object) Returns true iff object is a ValueGraph 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.

Method Detail

nodes

Set<N> nodes()

Returns all nodes in this graph, in the order specified by nodeOrder().

edges

Set<EndpointPair<N>> edges()

Returns all edges in this graph.

asGraph

Graph<N> asGraph()

Returns a live view of this graph as a Graph. The resulting Graph will have an edge connecting node A to node B if this ValueGraph has an edge connecting A to B.

isDirected

boolean isDirected()

Returns true if the edges in this graph are directed. Directed edges connect a source node to a target node, while undirected edges connect a pair of nodes to each other.

allowsSelfLoops

boolean allowsSelfLoops()

Returns true if this graph allows self-loops (edges that connect a node to itself). Attempting to add a self-loop to a graph that does not allow them will throw an IllegalArgumentException.

nodeOrder

ElementOrder<N> nodeOrder()

Returns the order of iteration for the elements of nodes().

adjacentNodes

Set<N> adjacentNodes(N node)

Returns the nodes which have an incident edge in common with node in this graph.

Throws:

IllegalArgumentException - if node is not an element of this graph

predecessors

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.

In an undirected graph, this is equivalent to adjacentNodes(Object).

Throws:

IllegalArgumentException - if node is not an element of this graph

successors

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.

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).

Throws:

IllegalArgumentException - if node is not an element of this graph

incidentEdges

Set<EndpointPair<N>> incidentEdges(N node)

Returns the edges in this graph whose endpoints include node.

Throws:

IllegalArgumentException - if node is not an element of this graph

Since:

24.0

degree

int degree(N node)

Returns the count of node's incident edges, counting self-loops 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 self-loops incident to node).

If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE.

Throws:

IllegalArgumentException - if node is not an element of this graph

inDegree

int inDegree(N node)

Returns the count of 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.

Throws:

IllegalArgumentException - if node is not an element of this graph

outDegree

int outDegree(N node)

Returns the count of 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.

Throws:

IllegalArgumentException - if node is not an element of this graph

hasEdgeConnecting

boolean hasEdgeConnecting(N nodeU,
                          N nodeV)

Returns true if there is an edge that directly connects 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).

Since:

23.0

hasEdgeConnecting

boolean hasEdgeConnecting(EndpointPair<N> endpoints)

Returns true if there is an edge that directly connects 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).

Since:

27.1

edgeValue

Optional<V> edgeValue(N nodeU,
                      N nodeV)

Returns the value of the edge that connects nodeU to nodeV (in the order, if any, specified by endpoints), if one is present; otherwise, returns Optional.empty().

Throws:

IllegalArgumentException - if nodeU or nodeV is not an element of this graph

Since:

23.0 (since 20.0 with return type V)

edgeValue

Optional<V> edgeValue(EndpointPair<N> endpoints)

Returns the value of the edge that connects endpoints (in the order, if any, specified by endpoints), if one is present; otherwise, returns Optional.empty().

If this graph is directed, the endpoints must be ordered.

Throws:

IllegalArgumentException - if either endpoint is not an element of this graph

IllegalArgumentException - if the endpoints are unordered and the graph is directed

Since:

27.1

edgeValueOrDefault

V edgeValueOrDefault(N nodeU,
                     N nodeV,
                     V defaultValue)

Returns the value of the edge that connects nodeU to nodeV, if one is present; otherwise, returns defaultValue.

In an undirected graph, this is equal to edgeValueOrDefault(nodeV, nodeU, defaultValue).

Throws:

IllegalArgumentException - if nodeU or nodeV is not an element of this graph

edgeValueOrDefault

V edgeValueOrDefault(EndpointPair<N> endpoints,
                     V defaultValue)

Returns the value of the edge that connects endpoints (in the order, if any, specified by endpoints), if one is present; otherwise, returns defaultValue.

If this graph is directed, the endpoints must be ordered.

Throws:

IllegalArgumentException - if either endpoint is not an element of this graph

IllegalArgumentException - if the endpoints are unordered and the graph is directed

Since:

27.1

equals

boolean equals(@Nullable Object object)

Returns true iff object is a ValueGraph that has the same elements and the same structural relationships as those in this graph.

Thus, two value 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.
• The value of a given edge is the same in both A and B.

Graph properties besides directedness do not affect equality. For example, two graphs may be considered equal even if one allows self-loops 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 AbstractValueGraph.equals(Object).

Overrides:

equals in class Object

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

hashCode

int hashCode()

Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a map from each of its edges to the associated edge value.

A reference implementation of this is provided by AbstractValueGraph.hashCode().

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)