Optimizing performance of HostId.
diff --git a/core/api/src/main/java/org/onlab/onos/net/DeviceId.java b/core/api/src/main/java/org/onlab/onos/net/DeviceId.java
index ef8c5ab..072ba28 100644
--- a/core/api/src/main/java/org/onlab/onos/net/DeviceId.java
+++ b/core/api/src/main/java/org/onlab/onos/net/DeviceId.java
@@ -1,15 +1,32 @@
 package org.onlab.onos.net;
 
 import java.net.URI;
+import java.util.Objects;
 
 /**
  * Immutable representation of a device identity.
  */
 public final class DeviceId extends ElementId {
 
+    /**
+     * Represents either no device, or an unspecified device.
+     */
+    public static final DeviceId NONE = deviceId("none:none");
+
+    private final URI uri;
+    private final String str;
+
     // Public construction is prohibited
     private DeviceId(URI uri) {
-        super(uri);
+        this.uri = uri;
+        this.str = uri.toString();
+    }
+
+
+    // Default constructor for serialization
+    protected DeviceId() {
+        this.uri = null;
+        this.str = null;
     }
 
     /**
@@ -30,4 +47,36 @@
         return deviceId(URI.create(string));
     }
 
+    /**
+     * Returns the backing URI.
+     *
+     * @return backing URI
+     */
+    public URI uri() {
+        return uri;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(str);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj instanceof DeviceId) {
+            final DeviceId that = (DeviceId) obj;
+            return this.getClass() == that.getClass() &&
+                    Objects.equals(this.str, that.str);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return str;
+    }
+
 }