[ONOS-8014] Add a set of interfaces for Kubernetes namespace

Change-Id: I2448e8ccd1bf3608710404fe8e9146ee1dfb6f9e
diff --git a/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sNamespaceEvent.java b/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sNamespaceEvent.java
new file mode 100644
index 0000000..f1e050c
--- /dev/null
+++ b/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sNamespaceEvent.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2019-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.k8snetworking.api;
+
+import io.fabric8.kubernetes.api.model.Namespace;
+import org.onosproject.event.AbstractEvent;
+
+/**
+ * Describes kubernetes namespace event.
+ */
+public class K8sNamespaceEvent extends AbstractEvent<K8sNamespaceEvent.Type, Namespace> {
+
+    /**
+     * Creates an event of a given type for the specified kubernetes namespace policy.
+     *
+     * @param type          kubernetes namespace event type
+     * @param subject       kubernetes namespace
+     */
+    public K8sNamespaceEvent(Type type, Namespace subject) {
+        super(type, subject);
+    }
+
+    /**
+     * Kubernetes namespace events.
+     */
+    public enum Type {
+
+        /**
+         * Signifies that a new kubernetes namespace is created.
+         */
+        K8S_NAMESPACE_CREATED,
+
+        /**
+         * Signifies that a new kubernetes namespace is updated.
+         */
+        K8S_NAMESPACE_UPDATED,
+
+        /**
+         * Signifies that a new kubernetes namespace is removed.
+         */
+        K8S_NAMESPACE_REMOVED,
+    }
+}