Bluebonnet

This is a partial implementation of the .NET platform on top of the Java Virtual Machine, and compatible with Android runtime. The Bluebonnet bytecode compiler translates .NET CIL into Java bytecode in Java classes, and additional run-time support is provided by the Baselib library.

https://www.spaceflint.com/bluebonnet

Highlights

• 100% Java 8 bytecode with no native code.
• Compatible with all Android API levels through desugaring.
• Runtime library translated from the .NET Base Class Library.
• Simple interoperability with Java APIs.
• Tested with C# and F# programs.

Requirements for Building

• Java 8 is required during building, to import Java classes from the rt.jar file.
  • Importing from Java 9 modules is not yet supported.
  • The translated code can run on Java 8 or later version.
  • Alternatively, (ANDROID_HOME)/platforms/android-XX/android.jar from Android SDK can be copied as (JAVA_HOME)\jre\lib\rt.jar file.
• Android build tools with support for D8/R8 desugaring.
  • Tested with build tools version 30.0.2 and platform API version 30.
• .NET Framework (4.7 or later)
  • Tested only on Windows at this time. May not necessarily build with .NET Core.

Recent releases include a pre-built Android.dll reference assembly, created from the latest Android SDK, as well as all binaries needed for running Bluebonnet. See the Usage section below.

Building

• Set JAVA_HOME environment variable to the Java 8 home directory.

• Open Bluebonnet.sln in Visual Studio 2017 or later, and build in Release configuration.

• Building from the command line is also possible:

  • Open a Visual Studio Developer command prompt.
  • Change to the solution directory.
  • Restore packages using nuget: nuget restore
  • Build the project: msbuild -p:Configuration=Release

• This should produce Bluebonnet.exe and Baselib.jar in the .obj sub-directory of the solution directory.

  • Bluebonnet.exe translates compiled .NET assemblies into Java classes.
  • Baselib.jar is required on the classpath when running the generated Java classes.

Demo

Building a simple Hello World example. The sample HelloWorld.cs in the Demos sub-directory uses parallel LINQ, so it exercises generics, delegates, and threads, among many other .NET features.

• Open a Visual Studio Developer command prompt.
• Make sure the JAVA_HOME environment variable is set properly.
• Change to the solution directory.
• Compile the demo: csc -out:.obj\HelloWorld.exe Demos\HelloWorld.cs
• Test the demo: .obj\HelloWorld.exe
  • It should print Hello, World!, one character at a time.
• Translate the demo: .obj\Bluebonnet .obj\HelloWorld.exe .obj\HelloWorld.jar
• Run the translation: "%JAVA_HOME%\bin\java" -classpath ".obj\HelloWorld.jar;.obj\Baselib.jar" spaceflint.demos.HelloWorld

Note that Java package names are lowercase, so .NET namespaces are translated to lowercase, e.g. SpaceFlint.Demos -> spaceflint.demos.

There are some additional demos:

• Change to the Demos directory inside the solution directory.
• Restore packages using nuget: nuget restore
• Build and run each demo: msbuild -p:Configuration=Release -t:RunDemo
  • Note that the Android demos require the ANDROID_HOME environment directory, and the project is hard-coded to use Android platform version 30, and build-tools 30.0.2
  • Note also that the Android demos build an APK file, but do not install it.

See the BNA and Unjum repositories for more demos for Android.

Usage

For more information about using Bluebonnet, please see the USAGE.md file. That document also records any known differences and deficiencies, compared to a proper .NET implementation. To use Bluebonnet in Android Studio, see USAGE-ANDROID.md.