diff --git a/api/module-lib-current.txt b/api/module-lib-current.txt
index 4787e11098f31..1a2cb74a5aad7 100644
--- a/api/module-lib-current.txt
+++ b/api/module-lib-current.txt
@@ -102,18 +102,18 @@ package android.timezone {
     method @NonNull public String getTimeZoneId();
   }
 
-  public class TelephonyLookup {
+  public final class TelephonyLookup {
     method @NonNull public static android.timezone.TelephonyLookup getInstance();
     method @Nullable public android.timezone.TelephonyNetworkFinder getTelephonyNetworkFinder();
   }
 
-  public class TelephonyNetwork {
+  public final class TelephonyNetwork {
     method @NonNull public String getCountryIsoCode();
     method @NonNull public String getMcc();
     method @NonNull public String getMnc();
   }
 
-  public class TelephonyNetworkFinder {
+  public final class TelephonyNetworkFinder {
     method @Nullable public android.timezone.TelephonyNetwork findNetworkByMccMnc(@NonNull String, @NonNull String);
   }
 
@@ -134,7 +134,7 @@ package android.timezone {
     method @NonNull public static android.timezone.TzDataSetVersion read() throws java.io.IOException, android.timezone.TzDataSetVersion.TzDataSetException;
   }
 
-  public static class TzDataSetVersion.TzDataSetException extends java.lang.Exception {
+  public static final class TzDataSetVersion.TzDataSetException extends java.lang.Exception {
     ctor public TzDataSetVersion.TzDataSetException(String);
     ctor public TzDataSetVersion.TzDataSetException(String, Throwable);
   }
diff --git a/core/java/android/timezone/TelephonyLookup.java b/core/java/android/timezone/TelephonyLookup.java
index eebccf4aa577a..8a5864e92db1a 100644
--- a/core/java/android/timezone/TelephonyLookup.java
+++ b/core/java/android/timezone/TelephonyLookup.java
@@ -30,9 +30,9 @@ import java.util.Objects;
  * @hide
  */
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
-public class TelephonyLookup {
+public final class TelephonyLookup {
 
-    private static Object sLock = new Object();
+    private static final Object sLock = new Object();
     @GuardedBy("sLock")
     private static TelephonyLookup sInstance;
 
diff --git a/core/java/android/timezone/TelephonyNetwork.java b/core/java/android/timezone/TelephonyNetwork.java
index ae39fbddfa1c5..487b3f2f143b0 100644
--- a/core/java/android/timezone/TelephonyNetwork.java
+++ b/core/java/android/timezone/TelephonyNetwork.java
@@ -27,7 +27,7 @@ import java.util.Objects;
  * @hide
  */
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
-public class TelephonyNetwork {
+public final class TelephonyNetwork {
 
     @NonNull
     private final libcore.timezone.TelephonyNetwork mDelegate;
diff --git a/core/java/android/timezone/TelephonyNetworkFinder.java b/core/java/android/timezone/TelephonyNetworkFinder.java
index 079d0882f1911..2ddd3d998d8eb 100644
--- a/core/java/android/timezone/TelephonyNetworkFinder.java
+++ b/core/java/android/timezone/TelephonyNetworkFinder.java
@@ -28,7 +28,7 @@ import java.util.Objects;
  * @hide
  */
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
-public class TelephonyNetworkFinder {
+public final class TelephonyNetworkFinder {
 
     @NonNull
     private final libcore.timezone.TelephonyNetworkFinder mDelegate;
diff --git a/core/java/android/timezone/TimeZoneFinder.java b/core/java/android/timezone/TimeZoneFinder.java
index 9327b001a9c84..c76bb1d1fd28b 100644
--- a/core/java/android/timezone/TimeZoneFinder.java
+++ b/core/java/android/timezone/TimeZoneFinder.java
@@ -32,7 +32,7 @@ import java.util.Objects;
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
 public final class TimeZoneFinder {
 
-    private static Object sLock = new Object();
+    private static final Object sLock = new Object();
     @GuardedBy("sLock")
     private static TimeZoneFinder sInstance;
 
diff --git a/core/java/android/timezone/TzDataSetVersion.java b/core/java/android/timezone/TzDataSetVersion.java
index aba7c4c159035..605155e76c2cb 100644
--- a/core/java/android/timezone/TzDataSetVersion.java
+++ b/core/java/android/timezone/TzDataSetVersion.java
@@ -89,7 +89,7 @@ public final class TzDataSetVersion {
      * @hide
      */
     @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
-    public static class TzDataSetException extends Exception {
+    public static final class TzDataSetException extends Exception {
 
         /** Creates an instance with a message. */
         public TzDataSetException(String message) {
diff --git a/core/java/android/timezone/ZoneInfoDb.java b/core/java/android/timezone/ZoneInfoDb.java
index 9d7094af1e180..4612a56df1178 100644
--- a/core/java/android/timezone/ZoneInfoDb.java
+++ b/core/java/android/timezone/ZoneInfoDb.java
@@ -32,7 +32,7 @@ import java.util.Objects;
 @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
 public final class ZoneInfoDb {
 
-    private static Object sLock = new Object();
+    private static final Object sLock = new Object();
     @GuardedBy("sLock")
     private static ZoneInfoDb sInstance;