Here comes the Sun

import java.util.ArrayList;
import java.util.Collection;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.GeometryCollection;
import com.vividsolutions.jts.geom.GeometryFactory;
import com.vividsolutions.jts.triangulate.DelaunayTriangulationBuilder;
import com.vividsolutions.jts.triangulate.VoronoiDiagramBuilder;

/**
 *
 * @author Sun Ning/SNDA
 * @since 2010-3-3
 */
public class DelaunayAndVoronoiApp {

    /**
     * create some predefined sites
     * @return
     */
    public static Collection<coordinate> getPredefinedSites(){
        double[][] coords = {{100,27},{28, 50},{29, 40},{32, 90}, {12, 26}};
        ArrayList<coordinate> coordinates = new ArrayList<coordinate>(coords.length);

        for(int i=0; i<coords.length; i++){
            coordinates.add(new Coordinate(coords[i][0], coords[i][1]));
        }

        return coordinates;
    }

    /**
     *
     * @param coords
     * @return a geometry collection of triangulations
     */
    public static Geometry buildDelaunayTriangulation(Collection<coordinate> coords){
        DelaunayTriangulationBuilder builder = new DelaunayTriangulationBuilder();
        builder.setSites(coords);
        return builder.getTriangles(new GeometryFactory());
    }
    /**
     *
     * @param coords
     * @return a collection of polygons
     */
    public static Geometry buildVoronoiDiagram(Collection<coordinate> coords){
        VoronoiDiagramBuilder builder = new VoronoiDiagramBuilder();
        builder.setSites(coords);
        return builder.getDiagram(new GeometryFactory());
    }

    /**
     *
     * @param args
     */
    public static void main(String[] args){
        Collection<coordinate> coordinates = getPredefinedSites();

        /**
         * Delauny
         */
        GeometryCollection triangulations
                = (GeometryCollection)buildDelaunayTriangulation(coordinates);

        int total = triangulations.getNumGeometries();
        System.out.printf("Total triangulations: %d\n", total);
        for(int i=0; i<total; i++){
            Geometry g = triangulations.getGeometryN(i);
            Coordinate[] coords = g.getCoordinates();
            System.out.printf("Triangulation %d: ", i);
            for(Coordinate c : coords){
                System.out.printf("(%.3f, %.3f) ", c.x, c.y);
            }
            System.out.println();
        }

        /**
         * Voronoi
         */
        GeometryCollection diagram = (GeometryCollection)
                buildVoronoiDiagram(coordinates);
        int totalDia = diagram.getNumGeometries();
        for(int i=0; i<totalDia; i++){
            Geometry g = diagram.getGeometryN(i);
            Coordinate[] coords = g.getCoordinates();
            System.out.printf("Diagram %d: ", i);
            for(Coordinate c : coords){
                System.out.printf("(%.3f, %.3f) ", c.x, c.y);
            }
            System.out.println();
        }
    }

}

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Shape;
import java.util.Collection;
import javax.swing.JFrame;
import javax.swing.JPanel;

import com.vividsolutions.jts.awt.ShapeWriter;
import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.Geometry;
import java.util.Random;

/**
 *
 * @author Sun Ning/SNDA
 * @since 2010-3-3
 */
public class JTS2Awt {

    public static void showUI(final Shape... shape){
        JFrame jframe = new JFrame("JTS Geometry to AWT Shape");

        JPanel jp = new JPanel(){
            @Override
            public void paint(Graphics g){
                super.paint(g);
                Graphics2D g2d = (Graphics2D)g;
                if(shape != null){
                    for(Shape s: shape){
                        g2d.setColor(new Color(Color.HSBtoRGB(new Random().nextFloat(), 1f, 0.6f)));
                        g2d.draw(s);
                    }
                }
            }
        };
        jp.setPreferredSize(new Dimension(150, 150));



        jframe.getContentPane().add(jp);
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.pack();
        jframe.setVisible(true);
    }

    public static Shape toShape(Geometry geom){
        ShapeWriter writer = new ShapeWriter();
        return writer.toShape(geom);
    }

    public static void main(String[] args){
        Collection<coordinate> coords = DelaunayAndVoronoiApp.getPredefinedSites();
        Geometry geomT = DelaunayAndVoronoiApp.buildDelaunayTriangulation(coords);
        Geometry geomD = DelaunayAndVoronoiApp.buildVoronoiDiagram(coords);

        showUI(toShape(geomT), toShape(geomD));
    }

}