Edge


1   /* Edge.java */
2   package org.quilt.graph;
3   
4   import org.quilt.exception.QuiltException;
5   
6   /** 
7    * An edge in a Quilt graph.  This is seen as a source/target pair,
8    * XXX but in fact the source field may be unnecessary.
9    *
10   * @author < a HREF="jddixon@users.sourceforge.net">Jim Dixon</a>
11   */
12  
13  public class Edge {
14  
15      protected Vertex source_;
16      protected Vertex target_; 
17   
18      /** 
19       * An edge in a directed graph.
20       */
21      public Edge(final Vertex s, final Vertex t) {
22          if ( s == null || t == null ) {
23              throw new IllegalArgumentException  ("null source or target");
24          }
25          if (s.getGraph() != t.getGraph() 
26                  && ! (s instanceof Exit || t instanceof Entry ) ) {
27              throw new IllegalArgumentException  ("source " + s 
28                      + " and target " + t + 
29                      " of edge constructor are not in the same graph");
30          }
31          source_ = s;
32          target_ = t;
33      }
34  
35      /** Copy constructor. */
36      public Edge ( final Edge e ) {
37          checkForNull (e, "edge");       
38          source_ = e.getSource();
39          target_ = e.getTarget();
40      }
41      // ACCESSOR METHODS /////////////////////////////////////////////
42      public Vertex getSource() {
43          return source_;
44      }
45      public void setSource (Vertex v) {
46          checkForNull(v, "source");
47          if (target_ != null && v.getGraph() != source_.getGraph()) {
48              throw new IllegalArgumentException  (
49                      "source and target must be in same graph");
50          }
51          source_ = v;
52      }
53      public Vertex getTarget() {
54          return target_;
55      }
56      /** 
57       * Change the target of this edge.  XXX Wasn't public before;
58       * made it so to allow cl.SortedBlocks to retarget to existing
59       * vertex.
60       */
61      public void setTarget (Vertex v) {
62          checkForNull(v, "target");
63          if ( !(source_ instanceof Exit || v instanceof Entry) 
64                              && (v.getGraph() != source_.getGraph())) {
65              /////////////////////////////////////////////////////////
66              // DEBUG -- this is a real problem but needs some thought.
67              // Fix it and put the exception back.
68              // //////////////////////////////////////////////////////
69              System.out.println("* WARNING * Edge {" + toString() 
70                  + "}\n    being retargeted to vertex " + v);
71              // END
72              //throw new IllegalArgumentException ("target in different graph");
73          }
74          target_ = v;
75      }
76      // OTHER METHODS ////////////////////////////////////////////////
77      public static void checkForNull(Object   o, String   what) {
78          if (o == null) {
79              throw new IllegalArgumentException   ("null " + what);
80          }
81      }
82      /** 
83       * @return the graph that this edge is in.
84       */
85      public Directed getGraph() {
86          return source_.getGraph();
87      }
88      /** 
89       * Insert a vertex with a UnaryConnector into an edge. 
90       *
91       * @param v The Vertex being inserted.
92       */
93      public void insert (Vertex v) {
94          checkForNull (v, "vertex");
95          if ( ! (source_.getGraph() == v.getGraph()) ) {
96              throw new IllegalArgumentException   (
97                      "vertex is in another graph");
98          }
99          Connector vConn = v.getConnector();
100         if (vConn == null) {
101             throw new IllegalArgumentException  (
102                     "internal error: vertex has null connector");
103         }
104         Vertex oldTarget = target_;
105         target_ = v;             // retarget this edge to v
106         vConn.setTarget(oldTarget);
107     }
108 
109     /** @return A String description of the edge, NOT newline-terminated. */
110     public String   toString () {
111         String   s = source_.toString() + " ---> " + target_;
112         return s;
113     }
114 }
115
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