Sync: consistently do not support inheritance

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/sync/SyncBuilder.java

@@ -35,7 +35,7 @@
  * {@link Sync#client(BoxStore, String, SyncCredentials)}.
  */
 @SuppressWarnings({"unused", "WeakerAccess"})
-public class SyncBuilder {
+public final class SyncBuilder {
 
     final Platform platform;
     final BoxStore boxStore;

objectbox-java/src/main/java/io/objectbox/sync/SyncClientImpl.java

@@ -38,7 +38,7 @@
  * this class may change without notice.
  */
 @Internal
-public class SyncClientImpl implements SyncClient {
+public final class SyncClientImpl implements SyncClient {
 
     @Nullable
     private BoxStore boxStore;

objectbox-java/src/main/java/io/objectbox/sync/server/ClusterPeerInfo.java

@@ -23,7 +23,7 @@
  * Internal class to keep configuration for a cluster peer.
  */
 @Internal
-class ClusterPeerInfo {
+final class ClusterPeerInfo {
     String url;
     SyncCredentialsToken credentials;
 

objectbox-java/src/main/java/io/objectbox/sync/server/SyncServerBuilder.java

@@ -37,7 +37,7 @@
  * Creates a {@link SyncServer} and allows to set additional configuration.
  */
 @SuppressWarnings({"unused", "UnusedReturnValue"})
-public class SyncServerBuilder {
+public final class SyncServerBuilder {
 
     final BoxStore boxStore;
     final URI url;

objectbox-java/src/main/java/io/objectbox/sync/server/SyncServerImpl.java

@@ -29,7 +29,7 @@
  * this class may change without notice.
  */
 @Internal
-public class SyncServerImpl implements SyncServer {
+public final class SyncServerImpl implements SyncServer {
 
     private final URI url;
     private volatile long handle;