Network (Guava: Google Core Libraries for Java 20.0-rc1 API)

Type Parameters:

N - Node parameter type

E - Edge parameter type

All Known Subinterfaces:

MutableNetwork<N,E>

All Known Implementing Classes:

AbstractNetwork, ImmutableNetwork
```
@Beta
public interface Network<N,E>
```
An interface for graph data structures. A graph is composed of a set of nodes (sometimes called vertices) and a set of edges connecting pairs of nodes. Graphs are useful for modeling many kinds of relations. If the relation to be modeled is symmetric (such as "distance between cities"), that can be represented with an undirected graph, where an edge that connects node U to node V also connects node V to node U. If the relation to be modeled is asymmetric (such as "employees managed"), that can be represented with a directed graph, where edges are strictly one-way.
There are three main 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.
1. Do you have data (objects) that you wish to associate with edges?
  Yes: Go to question 2. No: Use Graph.
2. Are the objects you wish to associate with edges unique within the scope of a graph? That is, no two objects would be equal to each other. A common example where this would not be the case is with weighted graphs.
  Yes: Go to question 3. No: Use ValueGraph.
3. Do you need to be able to query the graph for an edge associated with a particular object? For example, do you need to query what nodes an edge associated with a particular object connects, or whether an edge associated with that object exists in the graph?
  Yes: Use Network. No: Go to question 4.
4. Do you need explicit support for parallel edges? For example, do you need to remove one edge connecting a pair of nodes while leaving other edges connecting those same nodes intact?
  Yes: Use Network. No: Use ValueGraph.
Although MutableValueGraph and MutableNetwork both require users to provide objects to associate with edges when adding them, the differentiating factor is that in ValueGraphs, these objects can be any arbitrary data. Like the values in a Map, they do not have to be unique, and can be mutated while in the graph. In a Network, these objects serve as keys into the data structure. Like the keys in a Map, they must be unique, and cannot be mutated in a way that affects their equals/hashcode or the data structure will become corrupted.
In all three interfaces, nodes have all the same requirements as keys in a Map.
All mutation methods live on the subinterface MutableNetwork. If you do not need to mutate a network (e.g. if you write a method than runs a read-only algorithm on the network), you should prefer the non-mutating Network interface.
We provide an efficient implementation of this interface via NetworkBuilder. When using the implementation provided, all collection-returning methods provide live, unmodifiable views of the network. In other words, you cannot add an element to the collection, but if an element is added to the Network that would affect the collection, the collection will be updated automatically. This also means that you cannot mutate a Network in a way that would affect a collection while iterating over that collection. For example, you cannot remove either foo or any successors of foo from the network while iterating over successors(foo) (unless you first make a copy of the successors), just as you could not remove keys from a Map while iterating over its Map.keySet(). Behavior in such a case is undefined, and may result in ConcurrentModificationException.
Example of use:
```
 MutableNetwork roadNetwork = NetworkBuilder.undirected().build();
 roadNetwork.addEdge("Springfield", "Shelbyville", "Monorail");
 roadNetwork.addEdge("New York", "New New York", "Applied Cryogenics");
 roadNetwork.addEdge("Springfield", "New New York", "Secret Wormhole");
 String roadToQuery = "Secret Wormhole";
 if (roadNetwork.edges().contains(roadToQuery)) {
   EndpointPair cities = roadNetwork.incidentNodes(roadToQuery);
   System.out.format("%s and %s connected via %s", cities.nodeU(), cities.nodeV(), roadToQuery);
 }
 
```
Since:

20.0

Author:

James Sexton, Joshua O'Madadhain

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`Set<E>`	`adjacentEdges(Object edge)` Returns the edges which have an `incident node` in common with `edge`.
`Set<N>`	`adjacentNodes(Object node)` Returns the nodes which have an incident edge in common with `node` in this network.
`boolean`	`allowsParallelEdges()` Returns true if this network allows parallel edges.
`boolean`	`allowsSelfLoops()` Returns true if this network allows self-loops (edges that connect a node to itself).
`Graph<N>`	`asGraph()` Returns a live view of this network as a `Graph`.
`int`	`degree(Object node)` Returns the count of `node`'s `incident edges`, counting self-loops twice (equivalently, the number of times an edge touches `node`).
`ElementOrder<E>`	`edgeOrder()` Returns the order of iteration for the elements of `edges()`.
`Set<E>`	`edges()` Returns all edges in this network, in the order specified by `edgeOrder()`.
`Set<E>`	`edgesConnecting(Object nodeU, Object nodeV)` Returns the set of edges directly connecting `nodeU` to `nodeV`.
`boolean`	`equals(Object object)` For the default `Network` implementations, returns true iff `this == object` (reference equality).
`int`	`hashCode()` For the default `Network` implementations, returns `System.identityHashCode(this)`.
`Set<E>`	`incidentEdges(Object node)` Returns the edges whose `incident nodes` in this network include `node`.
`EndpointPair<N>`	`incidentNodes(Object edge)` Returns the nodes which are the endpoints of `edge` in this network.
`int`	`inDegree(Object node)` Returns the count of `node`'s `incoming edges` in a directed network.
`Set<E>`	`inEdges(Object node)` Returns all edges in this network which can be traversed in the direction (if any) of the edge to end at `node`.
`boolean`	`isDirected()` Returns true if the edges in this network are directed.
`ElementOrder<N>`	`nodeOrder()` Returns the order of iteration for the elements of `nodes()`.
`Set<N>`	`nodes()` Returns all nodes in this network, in the order specified by `nodeOrder()`.
`int`	`outDegree(Object node)` Returns the count of `node`'s `outgoing edges` in a directed network.
`Set<E>`	`outEdges(Object node)` Returns all edges in this network which can be traversed in the direction (if any) of the edge starting from `node`.
`Set<N>`	`predecessors(Object node)` Returns all nodes in this network adjacent to `node` which can be reached by traversing `node`'s incoming edges against the direction (if any) of the edge.
`Set<N>`	`successors(Object node)` Returns all nodes in this network 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 network, in the order specified by nodeOrder().
  - edges
```
Set<E> edges()
```
    Returns all edges in this network, in the order specified by edgeOrder().
  - asGraph
```
Graph<N> asGraph()
```
    Returns a live view of this network as a Graph. The resulting Graph will have an edge connecting node A to node B iff this Network has an edge connecting A to B.
    If this network allows parallel edges, parallel edges will be treated as if collapsed into a single edge. For example, the degree(Object) of a node in the Graph view may be less than the degree of the same node in this Network.
  - isDirected
```
boolean isDirected()
```
    Returns true if the edges in this network are directed. Directed edges connect a source node to a target node, while undirected edges connect a pair of nodes to each other.
  - allowsParallelEdges
```
boolean allowsParallelEdges()
```
    Returns true if this network allows parallel edges. Attempting to add a parallel edge to a network that does not allow them will throw an UnsupportedOperationException.
  - allowsSelfLoops
```
boolean allowsSelfLoops()
```
    Returns true if this network allows self-loops (edges that connect a node to itself). Attempting to add a self-loop to a network that does not allow them will throw an UnsupportedOperationException.
  - nodeOrder
```
ElementOrder<N> nodeOrder()
```
    Returns the order of iteration for the elements of nodes().
  - edgeOrder
```
ElementOrder<E> edgeOrder()
```
    Returns the order of iteration for the elements of edges().
  - adjacentNodes
```
Set<N> adjacentNodes(Object node)
```
    Returns the nodes which have an incident edge in common with node in this network.
    
    Throws:
    
    IllegalArgumentException - if node is not an element of this network
  - predecessors
```
Set<N> predecessors(Object node)
```
    Returns all nodes in this network adjacent to node which can be reached by traversing node's incoming edges against the direction (if any) of the edge.
    In an undirected network, this is equivalent to adjacentNodes(Object).
    
    Throws:
    
    IllegalArgumentException - if node is not an element of this network
  - successors
```
Set<N> successors(Object node)
```
    Returns all nodes in this network adjacent to node which can be reached by traversing node's outgoing edges in the direction (if any) of the edge.
    In an undirected network, 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 network
  - incidentEdges
```
Set<E> incidentEdges(Object node)
```
    Returns the edges whose incident nodes in this network include node.
    
    Throws:
    
    IllegalArgumentException - if node is not an element of this network
  - inEdges
```
Set<E> inEdges(Object node)
```
    Returns all edges in this network which can be traversed in the direction (if any) of the edge to end at node.
    In a directed network, an incoming edge's EndpointPair.target() equals node.
    In an undirected network, this is equivalent to incidentEdges(Object).
    
    Throws:
    
    IllegalArgumentException - if node is not an element of this network
  - outEdges
```
Set<E> outEdges(Object node)
```
    Returns all edges in this network which can be traversed in the direction (if any) of the edge starting from node.
    In a directed network, an outgoing edge's EndpointPair.source() equals node.
    In an undirected network, this is equivalent to incidentEdges(Object).
    
    Throws:
    
    IllegalArgumentException - if node is not an element of this network
  - degree
```
int degree(Object node)
```
    Returns the count of node's incident edges, counting self-loops twice (equivalently, the number of times an edge touches node).
    For directed networks, this is equal to inDegree(node) + outDegree(node).
    For undirected networks, 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 network
  - inDegree
```
int inDegree(Object node)
```
    Returns the count of node's incoming edges in a directed network. In an undirected network, 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 network
  - outDegree
```
int outDegree(Object node)
```
    Returns the count of node's outgoing edges in a directed network. In an undirected network, 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 network
  - incidentNodes
```
EndpointPair<N> incidentNodes(Object edge)
```
    Returns the nodes which are the endpoints of edge in this network.
    
    Throws:
    
    IllegalArgumentException - if edge is not an element of this network
  - adjacentEdges
```
Set<E> adjacentEdges(Object edge)
```
    Returns the edges which have an incident node in common with edge. An edge is not considered adjacent to itself.
    
    Throws:
    
    IllegalArgumentException - if edge is not an element of this network
  - edgesConnecting
```
Set<E> edgesConnecting(Object nodeU,
                       Object nodeV)
```
    Returns the set of edges directly connecting nodeU to nodeV.
    In an undirected network, this is equal to edgesConnecting(nodeV, nodeU).
    The resulting set of edges will be parallel (i.e. have equal incidentNodes(Object). If this network does not allow parallel edges, the resulting set will contain at most one edge.
    
    Throws:
    
    IllegalArgumentException - if nodeU or nodeV is not an element of this network
  - equals
```
boolean equals(@Nullable
               Object object)
```
    For the default Network implementations, returns true iff this == object (reference equality). External implementations are free to define this method as they see fit, as long as they satisfy the Object.equals(Object) contract.
    To compare two Networks based on their contents rather than their references, see Graphs.equivalent(Network, Network).
    
    Overrides:
    
    equals in class Object
  - hashCode
```
int hashCode()
```
    For the default Network implementations, returns System.identityHashCode(this). External implementations are free to define this method as they see fit, as long as they satisfy the Object.hashCode() contract.
    
    Overrides:
    
    hashCode in class Object

Interface Network<N,E>

Method Summary

Method Detail

nodes

edges

asGraph

isDirected

allowsParallelEdges

allowsSelfLoops

nodeOrder

edgeOrder

adjacentNodes

predecessors

successors

incidentEdges

inEdges

outEdges

degree

inDegree

outDegree

incidentNodes

adjacentEdges

edgesConnecting

equals

hashCode