Added graph-related utility code.
diff --git a/utils/misc/src/main/java/org/onlab/graph/AdjacencyListsGraph.java b/utils/misc/src/main/java/org/onlab/graph/AdjacencyListsGraph.java
new file mode 100644
index 0000000..a5a1300
--- /dev/null
+++ b/utils/misc/src/main/java/org/onlab/graph/AdjacencyListsGraph.java
@@ -0,0 +1,104 @@
+package org.onlab.graph;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSetMultimap;
+
+import java.util.Objects;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Immutable graph implemented using adjacency lists.
+ *
+ * @param <V> vertex type
+ * @param <E> edge type
+ */
+public class AdjacencyListsGraph<V extends Vertex, E extends Edge<V>> implements Graph<V, E> {
+
+ private final Set<V> vertexes;
+ private final Set<E> edges;
+
+ private final ImmutableSetMultimap<V, E> sources;
+ private final ImmutableSetMultimap<V, E> destinations;
+
+ private final Set<E> noEdges = ImmutableSet.of();
+
+ /**
+ * Creates a graph comprising of the specified vertexes and edges.
+ *
+ * @param vertexes set of graph vertexes
+ * @param edges set of graph edges
+ */
+ public AdjacencyListsGraph(Set<V> vertexes, Set<E> edges) {
+ checkNotNull(vertexes, "Vertex set cannot be null");
+ checkNotNull(edges, "Edge set cannot be null");
+
+ // Record ingress/egress edges for each vertex.
+ ImmutableSetMultimap.Builder<V, E> srcMap = ImmutableSetMultimap.builder();
+ ImmutableSetMultimap.Builder<V, E> dstMap = ImmutableSetMultimap.builder();
+
+ // Also make sure that all edge end-points are added as vertexes
+ ImmutableSet.Builder<V> actualVertexes = ImmutableSet.builder();
+ actualVertexes.addAll(vertexes);
+
+ for (E edge : edges) {
+ srcMap.put(edge.src(), edge);
+ actualVertexes.add(edge.src());
+ dstMap.put(edge.dst(), edge);
+ actualVertexes.add(edge.dst());
+ }
+
+ // Make an immutable copy of the edge and vertex sets
+ this.edges = ImmutableSet.copyOf(edges);
+ this.vertexes = actualVertexes.build();
+
+ // Build immutable copies of sources and destinations edge maps
+ sources = srcMap.build();
+ destinations = dstMap.build();
+ }
+
+ @Override
+ public Set<V> getVertexes() {
+ return vertexes;
+ }
+
+ @Override
+ public Set<E> getEdges() {
+ return edges;
+ }
+
+ @Override
+ public Set<E> getEdgesFrom(V src) {
+ return sources.get(src);
+ }
+
+ @Override
+ public Set<E> getEdgesTo(V dst) {
+ return destinations.get(dst);
+ }
+
+ @Override
+ public boolean equals(Object obj) {
+ if (obj instanceof AdjacencyListsGraph) {
+ AdjacencyListsGraph that = (AdjacencyListsGraph) obj;
+ return this.getClass() == that.getClass() &&
+ Objects.equals(this.vertexes, that.vertexes) &&
+ Objects.equals(this.edges, that.edges);
+ }
+ return false;
+ }
+
+ @Override
+ public int hashCode() {
+ return Objects.hash(vertexes, edges);
+ }
+
+ @Override
+ public String toString() {
+ return com.google.common.base.Objects.toStringHelper(this)
+ .add("vertexes", vertexes)
+ .add("edges", edges)
+ .toString();
+ }
+}