diff --git a/pkgs/jnigen/docs/interface_implementation.md b/pkgs/jnigen/docs/interface_implementation.md
index f96c10642..566824e78 100644
--- a/pkgs/jnigen/docs/interface_implementation.md
+++ b/pkgs/jnigen/docs/interface_implementation.md
@@ -36,7 +36,7 @@ class Runnable extends JObject {
   ) { /* ... */ }
 }
 
-abstract mixin class $Runnable {
+abstract base mixin class $Runnable {
   factory $Runnable({
     required void Function() run,
     bool run$async,
@@ -87,7 +87,7 @@ implementing the interface in Java instead of using the lambdas:
 
 ```java
 // Java
-public class Printer with Runnable {
+public class Printer implements Runnable {
   private final String text;
 
   public Printer(String text) {
@@ -108,7 +108,7 @@ You can do the same in Dart by creating a subclass that implements `$Runnable`:
 
 ```dart
 // Dart
-class Printer with $Runnable {
+final class Printer with $Runnable {
   final String text;
 
   Printer(this.text);
@@ -145,7 +145,7 @@ Similarly, when subclassing
 
 ```dart
 // Dart
-class Printer with $Runnable {
+final class Printer with $Runnable {
   final String text;
 
   Printer(this.text);
diff --git a/pkgs/jnigen/test/simple_package_test/runtime_test_registrant.dart b/pkgs/jnigen/test/simple_package_test/runtime_test_registrant.dart
index 41e9e22d0..fdabd98d5 100644
--- a/pkgs/jnigen/test/simple_package_test/runtime_test_registrant.dart
+++ b/pkgs/jnigen/test/simple_package_test/runtime_test_registrant.dart
@@ -993,7 +993,7 @@ void registerTests(String groupName, TestRunnerCallback test) {
   });
 }
 
-class DartStringToIntParser implements $StringConverter {
+final class DartStringToIntParser with $StringConverter {
   final int radix;
 
   DartStringToIntParser({required this.radix});
@@ -1004,7 +1004,7 @@ class DartStringToIntParser implements $StringConverter {
   }
 }
 
-class AsyncRunnable with $MyRunnable {
+final class AsyncRunnable with $MyRunnable {
   final Completer<void> completer;
 
   AsyncRunnable(this.completer);