org.jgrapht.graph.AsWeightedGraph Maven / Gradle / Ivy
/*
* (C) Copyright 2007-2018, by Lucas J Scharenbroich and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
package org.jgrapht.graph;
import org.jgrapht.*;
import java.io.*;
import java.util.*;
/**
* A weighted view of a graph.
*
*
* 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.
*
*
* 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.
*
*
* Note that edges returned by this graph's accessors are really just the edges of the underlying
* graph.
*
*
* This graph does not pass the hashCode and equals operations through to the backing graph,
* but relies on Object's equals and hashCode methods. This graph will be
* serializable if the backing graph is serializable.
*
* @param the graph vertex type
* @param the graph edge type
*
* @author Lucas J. Scharenbroich
* @since Sep 10, 2007
*/
public class AsWeightedGraph
extends
GraphDelegator
implements
Serializable,
Graph
{
private static final long serialVersionUID = 6408608293216853184L;
private final Map weightMap;
/**
* 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 g, Map weightMap)
{
super(g);
this.weightMap = Objects.requireNonNull(weightMap, "Weight map cannot be null");
}
/**
* {@inheritDoc}
*/
@Override
public void setEdgeWeight(E e, double weight)
{
if (super.getType().isWeighted()) {
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);
}
/**
* {@inheritDoc}
*/
@Override
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;
}
/**
* {@inheritDoc}
*/
@Override
public GraphType getType()
{
return super.getType().asWeighted();
}
}
// End AsWeightedGraph.java