structure
Interface Graph<V,E>

All Superinterfaces:

java.lang.Iterable<V>, Structure<V>

All Known Implementing Classes:

GraphList, GraphListDirected, GraphListUndirected, GraphMatrix, GraphMatrixDirected, GraphMatrixUndirected

public interface Graph<V,E>
extends Structure<V>

The interface describing all Graph objects. Graphs are collections of vertices connected by a set of edges. Edges may or may not be directed. Portions of the graph may be marked visited to support iterative algorithms. Iteration is provided over vertices, edges, and vertices adjacent to a particular vertex

Example usage:

To visit all of the vertices reachable from a given vertex we could use the following:

   static void reachableFrom(Graph g, Object vertexLabel)
   {
         g.visit(vertexLabel);       // visit this vertex

         // recursively visit unvisited neighbor vertices
         Iterator ni = g.neighbors(vertexLabel);
         while (ni.hasNext())
         {
             Object neighbor = ni.next(); // adjacent node label
             if (!g.isVisited(neighbor)x)
             {
                 reachableFrom(g,neighbor); // depth-first search
             } 
         }
   }
 

See Also:

GraphList, GraphMatrix

Method Summary

void	add(V label) Add a vertex to the graph
void	addEdge(V vtx1, V vtx2, E label) Add an edge between two vertices within the graph.
void	clear() Remove all vertices (and thus, edges) of the graph.
boolean	contains(V label) Test for vertex membership.
boolean	containsEdge(V vLabel1, V vLabel2) Test for edge membership.
int	degree(V label) Determine out degree of vertex.
int	edgeCount() Determine the number of edges in graph.
java.util.Iterator<Edge<V,E>>	edges() Construct an iterator over all edges.
V	get(V label) Get reference to actual label of vertex.
Edge<V,E>	getEdge(V label1, V label2) Get reference to actual edge.
boolean	isDirected() Determine if graph is directed.
boolean	isEmpty() Determine if graph is empty.
boolean	isVisited(V label) Return visited flag of vertex.
boolean	isVisitedEdge(Edge<V,E> e) Return visited flag of edge.
java.util.Iterator<V>	iterator() Construct vertex iterator.
java.util.Iterator<V>	neighbors(V label) Construct an adjacent vertex iterator.
V	remove(V label) Remove a vertex from the graph.
E	removeEdge(V vLabel1, V vLabel2) Remove possible edge between vertices labeled vLabel1 and vLabel2.
void	reset() Clear visited flags of edges and vertices.
int	size() Determine number of vertices within graph.
boolean	visit(V label) Test and set visited flag of vertex
boolean	visitEdge(Edge<V,E> e) Test and set visited flag of edge.

Methods inherited from interface structure.Structure

elements, values

Method Detail

add

void add(V label)

Add a vertex to the graph

Specified by:

add in interface Structure<V>

Parameters:

label - Label of the vertex; should be non-null

Pre:

label is a non-null label for vertex

Post:

a vertex with label is added to graph if vertex with label is already in graph, no action

addEdge

void addEdge(V vtx1,
             V vtx2,
             E label)

Add an edge between two vertices within the graph. Edge is directed iff graph is directed. Duplicate edges are silently replaced. Labels on edges may be null.

Parameters:

vtx1 - First (or source, if directed) vertex.

vtx2 - Second (or destination, if directed) vertex.

label - Label associated with the edge.

Pre:

vtx1 and vtx2 are labels of existing vertices

Post:

an edge (possibly directed) is inserted between vtx1 and vtx2.

remove

V remove(V label)

Remove a vertex from the graph. Associated edges are also removed. Non-vertices are silently ignored.

Specified by:

remove in interface Structure<V>

Parameters:

label - The label of the vertex within the graph.

Returns:

The label associated with the vertex.

Pre:

label is non-null vertex label

Post:

vertex with "equals" label is removed, if found

removeEdge

E removeEdge(V vLabel1,
             V vLabel2)

Remove possible edge between vertices labeled vLabel1 and vLabel2. Directed edges consider vLabel1 to be the source.

Parameters:

vLabel1 - First (or source, if directed) vertex.

vLabel2 - Second (or destination, if directed) vertex.

Returns:

The label associated with the edge removed.

Pre:

vLabel1 and vLabel2 are labels of existing vertices

Post:

edge is removed, its label is returned

get

V get(V label)

Get reference to actual label of vertex. Vertex labels are matched using their equals method, which may or may not test for actual equivalence. Result remains part of graph.

Parameters:

label - The label of the vertex sought.

Returns:

The actual label, or null if none is found.

Post:

returns actual label of indicated vertex

getEdge

Edge<V,E> getEdge(V label1,
                  V label2)

Get reference to actual edge. Edge is identified by the labels on associated vertices. If edge is directed, the label1 indicates source.

Parameters:

label1 - The first (or source, if directed) vertex.

label2 - The second (or destination, if directed) vertex.

Returns:

The edge, if found, or null.

Post:

returns actual edge between vertices

contains

boolean contains(V label)

Test for vertex membership.

Specified by:

contains in interface Structure<V>

Parameters:

label - The label of the vertex sought.

Returns:

True iff vertex with matching label is found.

Post:

returns true iff vertex with "equals" label exists

containsEdge

boolean containsEdge(V vLabel1,
                     V vLabel2)

Test for edge membership. If edges are directed, vLabel1 indicates source.

Parameters:

vLabel1 - First (or source, if directed) vertex.

vLabel2 - Second (or destination, if directed) vertex.

Returns:

True iff the edge exists within the graph.

Post:

returns true iff edge with "equals" label exists

visit

boolean visit(V label)

Test and set visited flag of vertex

Parameters:

label - Label of vertex to be visited.

Returns:

Previous value of visited flag on vertex.

Post:

sets visited flag on vertex, returns previous value

visitEdge

boolean visitEdge(Edge<V,E> e)

Test and set visited flag of edge.

Parameters:

e - Edge object that is part of graph.

Returns:

Previous value of the Edge's visited flag.

Pre:

sets visited flag on edge; returns previous value

isVisited

boolean isVisited(V label)

Return visited flag of vertex.

Parameters:

label - Label of vertex.

Returns:

True if vertex has been visited.

Post:

returns visited flag on labeled vertex

isVisitedEdge

boolean isVisitedEdge(Edge<V,E> e)

Return visited flag of edge.

Parameters:

e - Edge of graph to be considered.

Returns:

True if the edge has been visited.

Post:

returns visited flag on edge between vertices

reset

void reset()

Clear visited flags of edges and vertices.

Post:

resets visited flags to false

size

int size()

Determine number of vertices within graph.

Specified by:

size in interface Structure<V>

Returns:

The number of vertices within graph.

Post:

returns the number of vertices in graph

degree

int degree(V label)

Determine out degree of vertex.

Parameters:

label - Label associated with vertex.

Returns:

The number of edges with this vertex as source.

Pre:

label labels an existing vertex

Post:

returns the number of vertices adjacent to vertex

edgeCount

int edgeCount()

Determine the number of edges in graph.

Returns:

Number of edges in graph.

Post:

returns the number of edges in graph

iterator

java.util.Iterator<V> iterator()

Construct vertex iterator. Vertices are not visited in any guaranteed order.

Specified by:

iterator in interface java.lang.Iterable<V>

Specified by:

iterator in interface Structure<V>

Returns:

Iterator traversing vertices in graph.

See Also:

AbstractIterator, Iterator, Enumeration, Structure.elements()

Post:

returns iterator across all vertices of graph

neighbors

java.util.Iterator<V> neighbors(V label)

Construct an adjacent vertex iterator. Adjacent vertices (those on destination of edge, if directed) are considered, but not in any guaranteed order.

Parameters:

label - Label of the vertex.

Returns:

Iterator traversing the adjacent vertices of labeled vertex.

Pre:

label is label of vertex in graph

Post:

returns iterator over vertices adj. to vertex each edge beginning at label visited exactly once

edges

java.util.Iterator<Edge<V,E>> edges()

Construct an iterator over all edges. Every directed/undirected edge is considered exactly once. Order is not guaranteed.

Returns:

Iterator over edges.

Post:

returns iterator across edges of graph iterator returns edges; each edge visited once

clear

void clear()

Remove all vertices (and thus, edges) of the graph.

Specified by:

clear in interface Structure<V>

Post:

removes all vertices from graph

isEmpty

boolean isEmpty()

Determine if graph is empty.

Specified by:

isEmpty in interface Structure<V>

Returns:

True iff there are no vertices in graph.

Post:

returns true if graph contains no vertices

isDirected

boolean isDirected()

Determine if graph is directed.

Returns:

True iff the graph is directed.

Post:

returns true if edges of graph are directed