AsWeightedGraph.java

/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2007, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/*  ----------------------
 * AsWeightedGraph.java
 * ----------------------
 * (C) Copyright 2007, by Lucas J. Scharenbroich and Contributors.
 *
 * Original Author:  Lucas J. Scharenbroich
 * Contributor(s):   John V. Sichi
 *
 * $Id: AsWeightedGraph.java 562 2007-09-23 06:44:29Z perfecthash $
 *
 * Changes
 * -------
 * 10-Sep-2007 : Initial revision (LJS);
 *
 */
package org.jgrapht.graph;

import java.io.*;

import java.util.*;

import org.jgrapht.*;


/**
 * <p>A weighted view of the backing graph specified in the constructor. This
 * graph allows modules to apply algorithms designed for weighted graphs to an
 * unweighted graph by providing an explicit edge weight mapping. The
 * implementation also allows for "masking" weights for a subset of the edges in
 * an existing weighted graph.</p>
 *
 * <p>Query operations on this graph "read through" to the backing graph. Vertex
 * addition/removal and edge addition/removal are all supported (and immediately
 * reflected in the backing graph). Setting an edge weight will pass the
 * operation to the backing graph as well if the backing graph implements the
 * WeightedGraph interface. Setting an edge weight will modify the weight map in
 * order to maintain a consistent graph.</p>
 *
 * <p>Note that edges returned by this graph's accessors are really just the
 * edges of the underlying directed graph.</p>
 *
 * <p>This graph does <i>not</i> pass the hashCode and equals operations through
 * to the backing graph, but relies on <tt>Object</tt>'s <tt>equals</tt> and
 * <tt>hashCode</tt> methods. This graph will be serializable if the backing
 * graph is serializable.</p>
 *
 * @author Lucas J. Scharenbroich
 * @since Sep 10, 2007
 */
public class AsWeightedGraph<V, E>
    extends GraphDelegator<V, E>
    implements Serializable,
        WeightedGraph<V, E>
{
    //~ Static fields/initializers ---------------------------------------------

    /**
     */
    private static final long serialVersionUID = -716810639338971372L;

    //~ Instance fields --------------------------------------------------------

    protected final Map<E, Double> weightMap;
    private final boolean isWeightedGraph;

    //~ Constructors -----------------------------------------------------------

    /**
     * Constructor for AsWeightedGraph.
     *
     * @param g the backing graph over which a weighted view is to be created.
     * @param weightMap A mapping of edges to weights. If an edge is not present
     * in the weight map, the edge weight for the underlying graph is returned.
     * Note that a live reference to this map is retained, so if the caller
     * changes the map after construction, the changes will affect the
     * AsWeightedGraph instance as well.
     */
    public AsWeightedGraph(Graph<V, E> g, Map<E, Double> weightMap)
    {
        super(g);
        assert (weightMap != null);
        this.weightMap = weightMap;

        // Remember whether the backing graph implements the WeightedGraph
        // interface
        this.isWeightedGraph = (g instanceof WeightedGraph);
    }

    //~ Methods ----------------------------------------------------------------

    /**
     * @see WeightedGraph#setEdgeWeight
     */
    public void setEdgeWeight(E e, double weight)
    {
        if (isWeightedGraph) {
            super.setEdgeWeight(e, weight);
        }

        // Always modify the weight map.  It would be a terrible violation
        // of the use contract to silently ignore changes to the weights.
        weightMap.put(e, weight);
    }

    /**
     * @see Graph#getEdgeWeight
     */
    public double getEdgeWeight(E e)
    {
        double weight;

        // Always return the value from the weight map first and
        // only pass the call through as a backup
        if (weightMap.containsKey(e)) {
            weight = weightMap.get(e);
        } else {
            weight = super.getEdgeWeight(e);
        }

        return weight;
    }
}

// End AsWeightedGraph.java