Ensure a CompletedIntentUpdate subclass is the final state

Change-Id: Icecf8a45fad7cb80f3953dcfc081c344d3fa0adb

@@ -22,7 +22,7 @@ import static org.onosproject.net.intent.IntentState.FAILED;
 /**
  * Represents a phase where the compile has failed.
  */
-class CompilingFailed implements CompletedIntentUpdate {
+class CompilingFailed extends CompletedIntentUpdate {
 
     private final IntentData intentData;
 

@@ -22,12 +22,12 @@ import java.util.Optional;
 /**
  * Represents a completed phase of processing an intent.
  */
-interface CompletedIntentUpdate extends IntentUpdate {
+abstract class CompletedIntentUpdate implements IntentUpdate {
 
     @Override
-    default Optional<IntentUpdate> execute() {
+    public final Optional<IntentUpdate> execute() {
         return Optional.empty();
     }
 
-    IntentData data();
+    public abstract IntentData data();
 }

@@ -20,7 +20,7 @@ import org.onosproject.net.intent.IntentData;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static org.onosproject.net.intent.IntentState.INSTALLING;
 
-class Installed implements CompletedIntentUpdate {
+class Installed extends CompletedIntentUpdate {
 
     private final IntentData intentData;
 

@@ -20,7 +20,7 @@ import org.onosproject.net.intent.IntentData;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static org.onosproject.net.intent.IntentState.FAILED;
 
-class InstallingFailed implements CompletedIntentUpdate {
+class InstallingFailed extends CompletedIntentUpdate {
 
     private final IntentData intentData;
 

@@ -20,7 +20,7 @@ import org.onosproject.net.intent.IntentData;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static org.onosproject.net.intent.IntentState.WITHDRAWING;
 
-class Withdrawn implements CompletedIntentUpdate {
+class Withdrawn extends CompletedIntentUpdate {
 
     private final IntentData intentData;