--- /dev/null
+/*
+ * Copyright (c) 2003-2005 The BISON Project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+package peersim.graph;
+
+import java.util.*;
+
+/**
+* This class is an adaptor making any Graph an undirected graph
+* by making its edges bidirectional. The graph to be made undirected
+* is passed to the constructor. Only the reference is stored so
+* if the directed graph changes later, the undirected version will
+* follow that change. However, {@link #getNeighbours} has O(n) time complexity
+* (in other words, too slow for large graphs).
+* @see ConstUndirGraph
+*/
+public class UndirectedGraph implements Graph {
+
+
+// ====================== private fileds ========================
+// ==============================================================
+
+
+private final Graph g;
+
+
+// ====================== public constructors ===================
+// ==============================================================
+
+
+public UndirectedGraph( Graph g ) {
+
+ this.g = g;
+}
+
+
+// ======================= Graph implementations ================
+// ==============================================================
+
+
+public boolean isEdge(int i, int j) {
+
+ return g.isEdge(i,j) || g.isEdge(j,i);
+}
+
+// ---------------------------------------------------------------
+
+/**
+* Uses sets as collection so does not support multiple edges now, even if
+* the underlying directed graph does.
+*/
+public Collection<Integer> getNeighbours(int i) {
+
+ Set<Integer> result = new HashSet<Integer>();
+ result.addAll(g.getNeighbours(i));
+ final int max = g.size();
+ for(int j=0; j<max; ++j)
+ {
+ if( g.isEdge(j,i) ) result.add(j);
+ }
+
+ return Collections.unmodifiableCollection(result);
+}
+
+// ---------------------------------------------------------------
+
+public Object getNode(int i) { return g.getNode(i); }
+
+// ---------------------------------------------------------------
+
+/**
+* If there is an (i,j) edge, returns that, otherwise if there is a (j,i)
+* edge, returns that, otherwise returns null.
+*/
+public Object getEdge(int i, int j) {
+
+ if( g.isEdge(i,j) ) return g.getEdge(i,j);
+ if( g.isEdge(j,i) ) return g.getEdge(j,i);
+ return null;
+}
+
+// ---------------------------------------------------------------
+
+public int size() { return g.size(); }
+
+// --------------------------------------------------------------------
+
+public boolean directed() { return false; }
+
+// --------------------------------------------------------------------
+
+/** not supported */
+public boolean setEdge( int i, int j ) {
+
+ throw new UnsupportedOperationException();
+}
+
+// ---------------------------------------------------------------
+
+/** not supported */
+public boolean clearEdge( int i, int j ) {
+
+ throw new UnsupportedOperationException();
+}
+
+// --------------------------------------------------------------------
+
+public int degree(int i) {
+
+ return getNeighbours(i).size();
+}
+
+// --------------------------------------------------------------------
+/*
+public static void main( String[] args ) {
+
+
+ Graph net = null;
+ UndirectedGraph ug = new UndirectedGraph(net);
+ for(int i=0; i<net.size(); ++i)
+ System.err.println(i+" "+net.getNeighbours(i));
+ System.err.println("============");
+ for(int i=0; i<ug.size(); ++i)
+ System.err.println(i+" "+ug.getNeighbours(i));
+ for(int i=0; i<ug.size(); ++i)
+ {
+ for(int j=0; j<ug.size(); ++j)
+ System.err.print(ug.isEdge(i,j)?"W ":"- ");
+ System.err.println();
+ }
+
+ GraphIO.writeGML(net,System.out);
+}
+*/
+}
+
+
