simonrozsival · Oct 12, 2026
@@ -42,7 +42,7 @@ Additional context for code under `external/Java.Interop/`. This complements the
 - **`generator/`** — primary tool for generating C# bindings from Java API descriptions.
 - **`class-parse/`** — parses Java `.class` files and generates API descriptions.
 - **`java-source-utils/`** — utilities for processing Java source code.
-- **`jcw-gen/`** — generates Java Callable Wrapper classes.
+- Application Java Callable Wrappers are generated by `src/Microsoft.Android.Sdk.TrimmableTypeMap/`.
 - **`param-name-importer/`** — imports parameter names from Java source.
 
 ### Supporting libraries

@@ -27,7 +27,7 @@ These tests can be run immediately with `dotnet test` on the `.csproj`, even if
 | **java source** | `external/Java.Interop/tests/Java.Interop.Tools.JavaSource-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.JavaSource-Tests/Java.Interop.Tools.JavaSource-Tests.csproj -v minimal` |
 | **maven** | `external/Java.Interop/tests/Java.Interop.Tools.Maven-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.Maven-Tests/Java.Interop.Tools.Maven-Tests.csproj -v minimal` |
 | **api xml adjuster** | `external/Java.Interop/tests/Xamarin.Android.Tools.ApiXmlAdjuster-Tests/` | `dotnet test external/Java.Interop/tests/Xamarin.Android.Tools.ApiXmlAdjuster-Tests/Xamarin.Android.Tools.ApiXmlAdjuster-Tests.csproj -v minimal` |
-| **java callable wrappers** | `external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/Java.Interop.Tools.JavaCallableWrappers-Tests.csproj -v minimal` |
+| **Java peer naming/scanning** | `external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/Java.Interop.Tools.JavaCallableWrappers-Tests.csproj -v minimal` |
 | **java type system** | `external/Java.Interop/tests/Java.Interop.Tools.JavaTypeSystem-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.JavaTypeSystem-Tests/Java.Interop.Tools.JavaTypeSystem-Tests.csproj -v minimal` |
 | **expressions** | `external/Java.Interop/tests/Java.Interop.Tools.Expressions-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.Expressions-Tests/Java.Interop.Tools.Expressions-Tests.csproj -v minimal` ⚠️ Requires `javac` |
 | **generator tools** | `external/Java.Interop/tests/Java.Interop.Tools.Generator-Tests/` | `dotnet test external/Java.Interop/tests/Java.Interop.Tools.Generator-Tests/Java.Interop.Tools.Generator-Tests.csproj -v minimal` |
@@ -198,7 +198,7 @@ cause, or stack-trace extraction fails, while borrowed references remain valid.
 | Test Area | Assembly / Project | Notes |
 |-----------|--------------------|-------|
 | **generator** | `external/Java.Interop/tests/generator-Tests/` | Binding generator tests |
-| **java callable wrappers** | `external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/` | JCW generation |
+| **Java peer naming/scanning** | `external/Java.Interop/tests/Java.Interop.Tools.JavaCallableWrappers-Tests/` | Naming, scanning, and type-name mapping; current JCW generation is covered by the trimmable type map suites |
 | **java type system** | `external/Java.Interop/tests/Java.Interop.Tools.JavaTypeSystem-Tests/` | Java type system tooling |
 | **java source** | `external/Java.Interop/tests/Java.Interop.Tools.JavaSource-Tests/` | Java source generation |
 | **maven** | `external/Java.Interop/tests/Java.Interop.Tools.Maven-Tests/` | Maven integration |

@@ -82,6 +82,27 @@ The main outputs are:
 
 The app build also generates needed **platform JCWs** from framework inputs alongside user JCWs: for example, the [build tests](../../../src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/TrimmableTypeMapBuildTests.cs) check for `typemap/java/android/app/ActivityTracker.java` and its `Runtime.registerNatives` call. The [reference pack](../../../build-tools/create-packs/Microsoft.Android.Ref.proj) no longer ships prebuilt `mono.android.jar` or `mono.android.dex`. The handwritten Java runtime support instead comes from `java_runtime_trimmable.jar`, selected by [`_CollectRuntimeJarFilenames`](../../../src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets); this is not a jar of pre-generated platform JCWs. `ApplicationRegistration.java` is generated separately during the app build.
 
+The .NET 12 cleanup retires the standalone `jcw-gen` tool and the legacy public
+JCW emitter in `Java.Interop.Tools.JavaCallableWrappers`: its `CallableWrapper*`
+model/writers, reader/writer options, `JavaPeerStyle`, method classifier, and
+Cecil/XML import/export adapters. That emitter produced `__md_methods`,
+`Runtime.register`, and `TypeManager.Activate` references whose runtime
+implementations had already been removed. The assembly's shared naming,
+scanning, hashing, and type-name mapping utilities remain available, as does
+the supported XAJavaInterop1 **C# binding** generator. Application JCWs are
+generated exclusively by the trimmable pipeline.
+
+The SDK likewise ships only `java_runtime_trimmable.jar` and its DEX companion.
+The unused `java_runtime`, `java_runtime_fastdev`, `java_runtime_clr`, and
+`java_runtime_fastdev_clr` artifact pairs, Java `DebugRuntime`/`BuildConfig`
+classes, and old environment placeholder are retired. `Runtime.init`,
+`createNewContext`, `createNewContextWithData`, `switchToContext`,
+`destroyContexts`, `MonoPackageManager.setContext`, and `getDependencies`
+are no longer supplied. These are intentional tooling/bootstrap compatibility
+removals; custom build tools and Java sources must use the retained runtime
+artifact and current startup path. `Runtime.initInternal`, `registerNatives`,
+GC peers, and `ApplicationRegistration.Context` remain live.
+
 Each per-assembly TypeMap contains assembly-level mapping attributes: a key such as `my/app/MainActivity`, a proxy type, and, for a trimmable mapping, the managed target type. The root references the per-assembly maps via `TypeMapAssemblyTargetAttribute<T>`. The emitter writes **IL and metadata**, not `.cs` files; the C# in the sections below is an explanatory translation of emitted code, not a file that a developer should edit. See [`TypeMapAssemblyGenerator`](../../../src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyGenerator.cs), [`TypeMapAssemblyEmitter.EmitTypeMapAttribute`](../../../src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyEmitter.cs), and the [build-pipeline guide](../../../src/Microsoft.Android.Sdk.TrimmableTypeMap/README.md).
 
 For the example Activity, think of a mapping like this **conceptual C#**:
@@ -122,6 +143,15 @@ When JNI returns an object or Java passes one into managed code, [`TrimmableType
 
 The generated Java `onCreate` calls its native `n_OnCreate_Landroid_os_Bundle_`; constructors similarly declare generated `nctor_*` native callbacks, and instantiate/activate the managed peer when appropriate. The class's static block calls `mono.android.Runtime.registerNatives (MainActivity.class)` when the class is first initialized. This is **per Java class**. Application and instrumentation JCWs instead use a guarded `__md_registerNatives()` helper called from their generated wrappers: registration in their static initializer can be too early in startup. The declaration of `registerNatives(Class)` in [`mono.android.Runtime`](../../../src/java-runtime/java/mono/android/Runtime.java) is handwritten Java; individual JCWs and their registration calls are generated.
 
+Abstract JCWs retain their Java constructors and `super(...)` calls for
+subclasses, but do not declare or call native constructor bridges. Deferred
+Application/Instrumentation hierarchies also omit those bridges and their
+unused managed UCO constructor registrations; managed `CreateInstance`
+activation remains available. A deferred class with no non-constructor
+callbacks needs no lazy registration helper or flag. Callback-bearing
+deferred classes still use the helper, and nonempty native registration,
+concrete constructor guards, GC hooks, and startup registration remain intact.
+
 There is no concatenated `__md_methods` string and no `Runtime.register("managed.Type, Assembly", ...)` registration in this path. The old JNI native-symbol mangling rules (`Java_package_Class_method...`) matter for symbol-lookup-based JNI code, but generated app JCW callbacks here are associated with their Java declarations through [`RegisterNatives`](https://docs.oracle.com/en/java/javase/17/docs/specs/jni/functions.html#registernatives): the Java method **name** and **signature** must match; no `Java_...` export is required for each method.
 
 ### Runtime startup and registration handshake

@@ -72,7 +72,6 @@
     <Project Path="external/Java.Interop/src/Xamarin.Android.Tools.ApiXmlAdjuster/Xamarin.Android.Tools.ApiXmlAdjuster.csproj" />
     <Project Path="external/Java.Interop/tools/class-parse/class-parse.csproj" />
     <Project Path="external/Java.Interop/tools/java-source-utils/java-source-utils.csproj" />
-    <Project Path="external/Java.Interop/tools/jcw-gen/jcw-gen.csproj" />
     <Project Path="tools/relnote-gen/relnote-gen.csproj" />
     <Project Path="tools/tmt/tmt.csproj">
       <Platform Solution="*|Any CPU" Project="anycpu" />

@@ -58,16 +58,8 @@
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)NuGet.Versioning.dll" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)r8.jar" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)bundletool.jar" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime.jar" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_fastdev.jar" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_trimmable.jar" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime.dex" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_fastdev.dex" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_trimmable.dex" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_clr.jar" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_fastdev_clr.jar" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_clr.dex" />
-    <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)java_runtime_fastdev_clr.dex" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)manifestmerger.jar" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)proguard-android-optimize.txt" />
     <_MSBuildFiles Include="$(MicrosoftAndroidSdkOutDir)proguard-android.txt" />

@@ -9,14 +9,14 @@
   </Target>
   <Target Name="_GetJavaRuntimeJarPath">
     <PropertyGroup>
-      <_RuntimeJar_InTree>$([System.IO.Path]::GetFullPath ('$(XAInstallPrefix)'))\xbuild\Xamarin\Android\java_runtime.jar</_RuntimeJar_InTree>
-      <_RuntimeJar_System Condition=" '$(_XamarinAndroidMSBuildDirectory)' != '' ">$(_XamarinAndroidMSBuildDirectory)\java_runtime.jar</_RuntimeJar_System>
+      <_RuntimeJar_InTree>$([System.IO.Path]::GetFullPath ('$(XAInstallPrefix)'))\xbuild\Xamarin\Android\java_runtime_trimmable.jar</_RuntimeJar_InTree>
+      <_RuntimeJar_System Condition=" '$(_XamarinAndroidMSBuildDirectory)' != '' ">$(_XamarinAndroidMSBuildDirectory)\java_runtime_trimmable.jar</_RuntimeJar_System>
       <_JavaRuntimeJarPath Condition=" Exists($(_RuntimeJar_InTree)) ">$(_RuntimeJar_InTree)</_JavaRuntimeJarPath>
       <_JavaRuntimeJarPath Condition=" '$(_JavaRuntimeJarPath)' == '' and Exists($(_RuntimeJar_System)) ">$(_RuntimeJar_System)</_JavaRuntimeJarPath>
     </PropertyGroup>
     <Error
         Condition=" '$(_JavaRuntimeJarPath)' == '' "
-        Text="Could not determine path to `java_runtime.jar`."
+        Text="Could not determine path to `java_runtime_trimmable.jar`."
     />
   </Target>
   <Target Name="BuildTestJarFile"

@@ -37,7 +37,7 @@
     <!--
       Microsoft.SourceLink.GitHub is a build-time only package (PrivateAssets="All"), but its
       dependency Microsoft.Build.Tasks.Git 10.0.300 pulls System.IO.Hashing 10.0.8 in as a *runtime*
-      asset. Projects that only reference System.IO.Hashing transitively (e.g. class-parse, jcw-gen,
+      asset. Projects that only reference System.IO.Hashing transitively (e.g. class-parse,
       generator) therefore ship a System.IO.Hashing 10.0.8 assembly, which collides in the shared
       .NET for Android SDK pack `tools/` directory with the $(SystemIOHashingPackageVersion) assembly the
       build tasks are compiled against (System.IO.Hashing bumps its AssemblyVersion every patch),

@@ -41,7 +41,6 @@
     <Project Path="tools/class-parse/class-parse.csproj" />
     <Project Path="tools/generator/generator.csproj" />
     <Project Path="tools/java-source-utils/java-source-utils.csproj" />
-    <Project Path="tools/jcw-gen/jcw-gen.csproj" />
     <Project Path="tools/param-name-importer/param-name-importer.csproj" />
   </Folder>
 </Solution>
@@ -316,27 +316,6 @@ The following terms should not be translated: Metadata.xml, path.</comment>
     <value>JNI signature override '{0}' is invalid or does not match the parameter count for member '{1}'.</value>
     <comment>{0} - JNI method signature. {1} - .NET member.</comment>
   </data>
-  <data name="JavaCallableWrappers_XA4200" xml:space="preserve">
-    <value>Cannot generate Java wrapper for type '{0}'. Only 'class' types are supported.</value>
-    <comment>{0} - Java type.
-The following terms should not be translated:
-class.</comment>
-  </data>
-  <data name="JavaCallableWrappers_XA4201" xml:space="preserve">
-    <value>Cannot determine JNI name for type '{0}'.</value>
-    <comment>{0} - Java type.
-The following terms should not be translated: JNI.</comment>
-  </data>
-  <data name="JavaCallableWrappers_XA4203" xml:space="preserve">
-    <value>The 'Name' property must be a fully qualified type like 'com.example.MyClass' and no package was found for '{0}'.</value>
-    <comment>{0} - Java type.
-The following terms should not be translated:
-Name, com.example.MyClass.</comment>
-  </data>
-  <data name="JavaCallableWrappers_XA4204" xml:space="preserve">
-    <value>Unable to resolve interface type '{0}'. Are you missing an assembly reference?</value>
-    <comment>{0} - Java interface.</comment>
-  </data>
   <data name="JavaCallableWrappers_XA4205" xml:space="preserve">
     <value>[ExportField] can only be used on methods with 0 parameters.</value>
     <comment>The following terms should not be translated: [ExportField].</comment>
@@ -353,10 +332,6 @@ Name, com.example.MyClass.</comment>
     <value>[ExportField] cannot be used on a method returning 'void'.</value>
     <comment>The following terms should not be translated: [ExportField], void.</comment>
   </data>
-  <data name="JavaCallableWrappers_XA4217" xml:space="preserve">
-    <value>Cannot override Kotlin-generated method '{0}' because it is not a valid Java method name. This method can only be overridden from Kotlin.</value>
-    <comment>{0} - Kotlin method name.</comment>
-  </data>
   <data name="JniMarshalMethodGen_JM4001" xml:space="preserve">
     <value>Unable to preload reference '{0}'.</value>
     <comment>{0} - assembly path</comment>

@@ -91,10 +91,6 @@ namespace Java.Interop.Tools.Diagnostics {
 	//					XA4110	The registrar cannot marshal the out parameter of type `{0}` in signature for method `{1}`.
 	//					XA4111	The registrar cannot build a signature for type `{0}' in method `{1}`.
 	//			XA42xx	ACW generation
-	//					XA4200	Can only generate ACW's for `claas` types.
-	//					XA4201	Unable to determine JNI name for type {0}.
-	//					XA4203	The specified type name must be fully qualified.
-	//					XA4204	Unable to resolve interface type '{0}'. Are you missing an assembly reference?
 	//					XA4205	[ExportField] can only be used on methods with 0 parameters.
 	//					XA4206	[Export] cannot be used on a generic type.
 	//					XA4207	[ExportField] cannot be used on a generic type.
@@ -103,7 +99,6 @@ namespace Java.Interop.Tools.Diagnostics {
 	//					XA4210 "You need to add a reference to Mono.Android.Export.dll when you use ExportAttribute or ExportFieldAttribute."
 	//					XA4211  AndroidManifest.xml //uses-sdk/@android:targetSdkVersion '{0}' is less than $(TargetFrameworkVersion) '{1}'. Using API-{1} for ACW compilation.
 	//					XA4212  Type `{0}` implements `Android.Runtime.IJavaObject` but does not inherit `Java.Lang.Object` or `Java.Lang.Throwable`. This is not supported.
-	//					XA4217  Cannot override Kotlin-generated method '{0}' because it is not a valid Java method name. This method can only be overridden from Kotlin."
 	// XA5xxx	GCC and toolchain
 	//			XA32xx	.apk generation
 	//					XA4300  Unsupported $(AndroidSupportedAbis) value '{0}'; ignoring.
@@ -195,4 +190,3 @@ public static Action<TraceLevel, string> CreateConsoleLogger ()
 		}
 	}
 }
-