--- /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 for representing subgraphs of any graph.
+* The subgraph is defined the following way.
+* The subgraph always contains all the nodes of the original underlying
+* graph. However, it is possible to remove edges by flagging nodes as
+* removed, in which case
+* the edges that have at least one end on those nodes are removed.
+* If the underlying graph changes after initialization, this class follows
+* the change.
+*/
+public class SubGraphEdges implements Graph {
+
+
+// ====================== private fields ========================
+// ==============================================================
+
+
+private final Graph g;
+
+private final BitSet nodes;
+
+
+// ====================== public constructors ===================
+// ==============================================================
+
+
+/**
+* Constructs an initially empty subgraph of g. That is, the subgraph will
+* contain no nodes.
+*/
+public SubGraphEdges( Graph g ) {
+
+ this.g = g;
+ nodes = new BitSet(g.size());
+}
+
+
+// ======================= Graph implementations ================
+// ==============================================================
+
+
+public boolean isEdge(int i, int j) {
+
+ return nodes.get(i) && nodes.get(j) && g.isEdge(i,j);
+}
+
+// ---------------------------------------------------------------
+
+public Collection<Integer> getNeighbours(int i) {
+
+ List<Integer> result = new LinkedList<Integer>();
+ if( nodes.get(i) )
+ {
+ for(Integer in:g.getNeighbours(i))
+ {
+ if( nodes.get(in) ) result.add(in);
+ }
+ }
+
+ return Collections.unmodifiableCollection(result);
+}
+
+// ---------------------------------------------------------------
+
+public Object getNode(int i) { return g.getNode(i); }
+
+// ---------------------------------------------------------------
+
+/**
+* If both i and j are within the node set of the subgraph and the original
+* graph has an (i,j) edge, returns that edge.
+*/
+public Object getEdge(int i, int j) {
+
+ if( isEdge(i,j) ) return g.getEdge(i,j);
+ return null;
+}
+
+// --------------------------------------------------------------------
+
+public int size() { return g.size(); }
+
+// --------------------------------------------------------------------
+
+public boolean directed() { return g.directed(); }
+
+// --------------------------------------------------------------------
+
+/** 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) {
+
+ int degree=0;
+ if( nodes.get(i) )
+ {
+ for(Integer in:g.getNeighbours(i))
+ {
+ if( nodes.get(in) ) degree++;
+ }
+ }
+ return degree;
+}
+
+
+// ================= public functions =================================
+// ====================================================================
+
+
+/**
+* This function returns the size of the subgraph, i.e. the number of nodes
+* in the subgraph.
+*/
+public int subGraphSize() { return nodes.cardinality(); }
+
+// --------------------------------------------------------------------
+
+/**
+* Removes given node from subgraph.
+* @return true if the node was already in the subgraph otherwise false.
+*/
+public boolean removeNode(int i) {
+
+ boolean was = nodes.get(i);
+ nodes.clear(i);
+ return was;
+}
+
+// --------------------------------------------------------------------
+
+/**
+* Adds given node to subgraph.
+* @return true if the node was already in the subgraph otherwise false.
+*/
+public boolean addNode(int i) {
+
+ boolean was = nodes.get(i);
+ nodes.set(i);
+ return was;
+}
+}
+
