Allow NextObjective to refer to another NextObjective by NextId

Change-Id: I4bc5381be8241ddd765668275f02f795ba06a632
(cherry picked from commit 7fbd2b167ac2a8981255dc17aa53b2ba93073018)
(cherry picked from commit f261d5cbaf8e936b5e3b2f0c55d8e9e698922d2d)
diff --git a/core/api/src/main/java/org/onosproject/net/flowobjective/DefaultNextTreatment.java b/core/api/src/main/java/org/onosproject/net/flowobjective/DefaultNextTreatment.java
new file mode 100644
index 0000000..4387b56
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/flowobjective/DefaultNextTreatment.java
@@ -0,0 +1,81 @@
+/*
+ * Copyright 2018-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.net.flowobjective;
+
+import org.onosproject.net.flow.TrafficTreatment;
+
+import java.util.Objects;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
+
+/**
+ * Represents a next action specified by traffic treatment.
+ */
+public final class DefaultNextTreatment implements NextTreatment {
+    private final TrafficTreatment treatment;
+
+    private DefaultNextTreatment(TrafficTreatment treatment) {
+        this.treatment = treatment;
+    }
+
+    /**
+     * Returns traffic treatment.
+     *
+     * @return traffic treatment.
+     */
+    public TrafficTreatment treatment() {
+        return treatment;
+    }
+
+    /**
+     * Returns an instance of DefaultNextTreatment with given traffic treatment.
+     *
+     * @param treatment traffic treatment
+     * @return an instance of DefaultNextTreatment
+     */
+    public static DefaultNextTreatment of(TrafficTreatment treatment) {
+        return new DefaultNextTreatment(treatment);
+    }
+
+    @Override
+    public Type type() {
+        return Type.TREATMENT;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(treatment);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj instanceof DefaultNextTreatment) {
+            final DefaultNextTreatment other = (DefaultNextTreatment) obj;
+            return Objects.equals(this.treatment, other.treatment);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this)
+                .add("treatment", treatment)
+                .toString();
+    }
+}