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JTS Topology Suite 1.14 with additional functions for GeoSpark
There is a newer version: 0.1.4

/*
 * The JTS Topology Suite is a collection of Java classes that
 * implement the fundamental operations required to validate a given
 * geo-spatial data set to a known topological specification.
 *
 * Copyright (C) 2001 Vivid Solutions
 *
 * 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
 *
 * For more information, contact:
 *
 *     Vivid Solutions
 *     Suite #1A
 *     2328 Government Street
 *     Victoria BC  V8T 5G5
 *     Canada
 *
 *     (250)385-6040
 *     www.vividsolutions.com
 */


package com.vividsolutions.jts.planargraph;

import java.util.*;
import com.vividsolutions.jts.geom.Coordinate;

/**
 * A sorted collection of {@link DirectedEdge}s which leave a {@link Node}
 * in a {@link PlanarGraph}.
 *
 * @version 1.7
 */
public class DirectedEdgeStar
{

  /**
   * The underlying list of outgoing DirectedEdges
   */
  protected List outEdges = new ArrayList();
  private boolean sorted = false;

  /**
   * Constructs a DirectedEdgeStar with no edges.
   */
  public DirectedEdgeStar() {
  }
  /**
   * Adds a new member to this DirectedEdgeStar.
   */
  public void add(DirectedEdge de)
  {
    outEdges.add(de);
    sorted = false;
  }
  /**
   * Drops a member of this DirectedEdgeStar.
   */
  public void remove(DirectedEdge de)
  {
    outEdges.remove(de);
  }
  /**
   * Returns an Iterator over the DirectedEdges, in ascending order by angle with the positive x-axis.
   */
  public Iterator iterator()
  {
    sortEdges();
    return outEdges.iterator();
  }

  /**
   * Returns the number of edges around the Node associated with this DirectedEdgeStar.
   */
  public int getDegree() { return outEdges.size(); }

  /**
   * Returns the coordinate for the node at wich this star is based
   */
  public Coordinate getCoordinate()
  {
    Iterator it = iterator();
    if (! it.hasNext()) return null;
    DirectedEdge e = (DirectedEdge) it.next();
    return e.getCoordinate();
  }

  /**
   * Returns the DirectedEdges, in ascending order by angle with the positive x-axis.
   */
  public List getEdges()
  {
    sortEdges();
    return outEdges;
  }

  private void sortEdges()
  {
    if (! sorted) {
      Collections.sort(outEdges);
      sorted = true;
    }
  }
  /**
   * Returns the zero-based index of the given Edge, after sorting in ascending order
   * by angle with the positive x-axis.
   */
  public int getIndex(Edge edge)
  {
    sortEdges();
    for (int i = 0; i < outEdges.size(); i++) {
      DirectedEdge de = (DirectedEdge) outEdges.get(i);
      if (de.getEdge() == edge)
        return i;
    }
    return -1;
  }
  /**
   * Returns the zero-based index of the given DirectedEdge, after sorting in ascending order
   * by angle with the positive x-axis.
   */  
  public int getIndex(DirectedEdge dirEdge)
  {
    sortEdges();
    for (int i = 0; i < outEdges.size(); i++) {
      DirectedEdge de = (DirectedEdge) outEdges.get(i);
      if (de == dirEdge)
        return i;
    }
    return -1;
  }
  /**
   * Returns value of i modulo the number of edges in this DirectedEdgeStar
   * (i.e. the remainder when i is divided by the number of edges)
   * 
   * @param i an integer (positive, negative or zero)
   */
  public int getIndex(int i)
  {
    int modi = i % outEdges.size();
    //I don't think modi can be 0 (assuming i is positive) [Jon Aquino 10/28/2003] 
    if (modi < 0) modi += outEdges.size();
    return modi;
  }

  /**
   * Returns the {@link DirectedEdge} on the left-hand (CCW) 
   * side of the given {@link DirectedEdge} 
   * (which must be a member of this DirectedEdgeStar). 
   */
  public DirectedEdge getNextEdge(DirectedEdge dirEdge)
  {
    int i = getIndex(dirEdge);
    return (DirectedEdge) outEdges.get(getIndex(i + 1));
  }
  
  /**
   * Returns the {@link DirectedEdge} on the right-hand (CW) 
   * side of the given {@link DirectedEdge} 
   * (which must be a member of this DirectedEdgeStar). 
   */
  public DirectedEdge getNextCWEdge(DirectedEdge dirEdge)
  {
    int i = getIndex(dirEdge);
    return (DirectedEdge) outEdges.get(getIndex(i - 1));
  }
}