package org.apache.commons.graph;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

/**
 * Describes an edge between two vertices of a graph, i.e. a relation between
 * two arbitrary vertices.
 *
 * @version $Id: Edge.java,v 1.1 2001/11/12 16:05:18 jvanzyl Exp $
 * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
 */
public class Edge implements Cloneable, Constants, java.io.Serializable {
  private int        ident;   // unique number, i.e. identifier
  private static int counter; // produce default numbers

  /**
   * Create edge.
   */
  public Edge() {
    ident = counter++;
  }

  /**
   * @return ident, i.e. identifier of this node
   */
  public final int getIdent()  { return ident; }

  /**
   * @return number of created edges
   */
  public static final int getCounter()  { return counter; }

  /**
   * @return String representation.
   */ 
  public String toString() {
    return toString(PLAIN);
  }
 
  /**
   * @param verbose toggle output format
   * @return String representation.
   */
  public String toString(int verbose) {
    if((verbose == TALKATIVE) || (verbose == V_TALKATIVE))
      return "Edge(" + ident + ")";

    return "";
  }

  /**
   * Access for visitor patterns
   */
  public void accept(Visitor v) { v.discoverEdge(this); }

  /**
   * @return deep copy
   */
  public Edge copy() {
    try {
      return (Edge)clone();
    } catch(CloneNotSupportedException e) {}

    return null;
  }

  /** Check for equality.
   */
  public boolean equals(Object o) {
    if(!(o instanceof Edge))
      return false;

    Edge e = (Edge)o;
    return e.ident == ident;
  }
}