001    /**
002     * Copyright (c) 2003 Daffodil Software Ltd all rights reserved,
003     * Modifications Copyright (c) 2008 Regiscope Digital Imaging Co, LLC, All rights reserved.
004     * This program is free software; you can redistribute it and/or modify
005     * it under the terms of version 2 of the GNU General Public License as
006     * published by the Free Software Foundation.
007     * There are special exceptions to the terms and conditions of the GPL
008     * as it is applied to this software. See the GNU General Public License for more details.
009     *
010     * This program is distributed in the hope that it will be useful,
011     * but WITHOUT ANY WARRANTY; without even the implied warranty of
012     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
013     * GNU General Public License for more details.
014     *
015     * You should have received a copy of the GNU General Public License
016     * along with this program; if not, write to the Free Software
017     * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
018     */
019    
020    package org.dbreplicator.graph;
021    
022        /**
023            Instances of this class act as elements of a linked list. It is used for keeping
024            <CODE>JbVertex</CODE>-instances and <CODE>JbEdge</CODE>-instances in order.
025            <UL><LI>The collision management strategy of the hash table,</LI>
026            <LI>the general vertex list of the graph,</LI>
027            <LI>and the edges of a single vertex</LI>
028            </UL>are all kept in a linked list of of <CODE>JbListElement</CODE> instances.
029        */
030    
031        public class JbListElement{
032    
033            //-----------
034            // Variables
035            //-----------
036    
037            /**
038                    A link to the next element in the linked list.
039            */
040            public JbListElement next;
041    
042            /**
043                    A link to the actual object represented by this "hanger" instance.
044                    Usually an instance of <CODE>JbVertex</CODE> or <CODE>JbEdge</CODE>.
045            */
046            public Object hangingVertexOrEdge;
047    
048            //--------------
049            // Constructor
050            //--------------
051    
052            /**
053                    The null constructor gets called when we
054                    initialize the hash table. We attach null-
055                    containing-list elements to each hash index, for
056                    ease of coding. (If you want to understand why
057                    this is important, try to visualize the return
058                    value of the method <CODE>findVertex</CODE>
059                    without guarantee that each index in the hash
060                    table will have at least one
061                    <CODE>JbListElement</CODE>...)
062            */
063    
064            public JbListElement(){
065              next=null;
066              hangingVertexOrEdge=null;
067            }
068    
069            /**
070                    The list element is a general linked list
071                    element. It contains a link to the next element,
072                    and a hanger for the vertex or the edge that
073                    it represents.
074                    @param objToHang The object that we wish to "hang"
075                    in this list element, usually an instance of
076                    <CODE>JbVertex</CODE> or <CODE>JbEdge</CODE>
077            */
078    
079            public JbListElement(Object objToHang){
080              next=null;
081              hangingVertexOrEdge=objToHang;
082            }
083    
084            //------------
085            // Methods
086            //------------
087            public String toString(){
088              String str=hangingVertexOrEdge.toString();
089              String s=str;
090              JbListElement le= this;
091              while(s!=null){
092                le= le.next;
093                if(le!=null)
094                str+=le.hangingVertexOrEdge;
095              else
096                  s=null;
097              }
098              return str;
099            }
100        }
101