Refactor CompareResult<> class and its call sites

Move all corner case logic from call sites to CompareResult's implementation,
add a constructor to directly do the comparison.

Test: runtest frameworks-core -c android.net.LinkPropertiesTest
Change-Id: I95bba82ec38d295b18c49c025dffab5f17271cbd
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 1703bd5..cee81a8 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -4435,12 +4435,9 @@
 
     private void updateInterfaces(LinkProperties newLp, LinkProperties oldLp, int netId,
                                   NetworkCapabilities caps) {
-        CompareResult<String> interfaceDiff = new CompareResult<String>();
-        if (oldLp != null) {
-            interfaceDiff = oldLp.compareAllInterfaceNames(newLp);
-        } else if (newLp != null) {
-            interfaceDiff.added = newLp.getAllInterfaceNames();
-        }
+        CompareResult<String> interfaceDiff = new CompareResult<String>(
+                oldLp != null ? oldLp.getAllInterfaceNames() : null,
+                newLp != null ? newLp.getAllInterfaceNames() : null);
         for (String iface : interfaceDiff.added) {
             try {
                 if (DBG) log("Adding iface " + iface + " to network " + netId);
@@ -4466,12 +4463,10 @@
      * @return true if routes changed between oldLp and newLp
      */
     private boolean updateRoutes(LinkProperties newLp, LinkProperties oldLp, int netId) {
-        CompareResult<RouteInfo> routeDiff = new CompareResult<RouteInfo>();
-        if (oldLp != null) {
-            routeDiff = oldLp.compareAllRoutes(newLp);
-        } else if (newLp != null) {
-            routeDiff.added = newLp.getAllRoutes();
-        }
+        // Compare the route diff to determine which routes should be added and removed.
+        CompareResult<RouteInfo> routeDiff = new CompareResult<RouteInfo>(
+                oldLp != null ? oldLp.getAllRoutes() : null,
+                newLp != null ? newLp.getAllRoutes() : null);
 
         // add routes before removing old in case it helps with continuous connectivity