edu.uci.ics.jung.graph.predicates.ConnectedGraphPredicate.java Source code

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Here is the source code for edu.uci.ics.jung.graph.predicates.ConnectedGraphPredicate.java

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/*
* Copyright (c) 2003, the JUNG Project and the Regents of the University 
* of California
* All rights reserved.
*
* This software is open-source under the BSD license; see either
* "license.txt" or
* http://jung.sourceforge.net/license.txt for a description.
* 
* Created on Mar 3, 2004
*/
package edu.uci.ics.jung.graph.predicates;

import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Set;

import edu.uci.ics.jung.graph.ArchetypeGraph;
import edu.uci.ics.jung.graph.Graph;
import edu.uci.ics.jung.graph.Vertex;

/**
 * 
 * @author Joshua O'Madadhain
 */
public class ConnectedGraphPredicate extends GraphPredicate {
    private static ConnectedGraphPredicate instance;
    private static String message = "connected graph predicate";

    /**
     * Returns an instance of this class.
     */
    public static ConnectedGraphPredicate getInstance() {
        if (instance == null)
            instance = new ConnectedGraphPredicate();
        return instance;
    }

    protected ConnectedGraphPredicate() {
        super();
    }

    public String toString() {
        return message;
    }

    /**
     * Returns <code>true</code> if there exists a path from each 
     * vertex to all other vertices (ignoring edge direction).
     * 
     * <p>Returns <code>true</code> for an empty graph.</p>
     * 
     * @see org.apache.commons.collections.Predicate#evaluate(java.lang.Object)
     */
    public boolean evaluateGraph(ArchetypeGraph graph) {
        Graph g = (Graph) graph;
        if (g.numVertices() == 0)
            return true;

        Vertex start = (Vertex) g.getVertices().iterator().next(); // pick any vertex
        Set visited = new HashSet();
        LinkedList stack = new LinkedList();
        stack.add(start);
        // traverse through graph in depth-first order
        while (!stack.isEmpty()) {
            Vertex v = (Vertex) stack.removeFirst();
            visited.add(v);
            Set neighbors = v.getNeighbors();
            for (Iterator n_it = neighbors.iterator(); n_it.hasNext();) {
                Vertex w = (Vertex) n_it.next();
                if (!visited.contains(w))
                    stack.addFirst(w);
            }
        }
        return (visited.size() == g.numVertices());
    }
}