Implement DeviceImpl and Path class, and minor change

Change-Id: I666d6d7e00620220048c5f8031a7c7c149ec89cd
diff --git a/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Path.java b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Path.java
new file mode 100644
index 0000000..4666345
--- /dev/null
+++ b/src/main/java/net/onrc/onos/ofcontroller/networkgraph/Path.java
@@ -0,0 +1,24 @@
+package net.onrc.onos.ofcontroller.networkgraph;
+
+import java.util.Iterator;
+import java.util.LinkedList;
+
+/**
+ * Base class for Path representation
+ * @author Toshio Koide (t-koide@onlab.us)
+ */
+public class Path extends LinkedList<Link> {
+	private static final long serialVersionUID = 7127274096495173415L;
+	
+	@Override
+	public String toString() {
+		StringBuilder builder = new StringBuilder();
+		Iterator<Link> i = this.iterator();
+		while (i.hasNext()) {
+			builder.append(i.next().toString());
+			if (i.hasNext())
+				builder.append(", ");
+		}
+		return builder.toString();
+	}
+}