A demonstration Android application showcasing different approaches to Java Native Interface (JNI) implementation and native code integration in Android applications.

This project demonstrates various ways to integrate native code with Android applications using JNI. It includes examples of:

• Standard JNI implementation
• JNI with a custom generator
• Integration with external build systems (Bazel)
• Different native build approaches (CMake, ndk-build, Bazel)

The app displays a simple UI where users can enter their name and see greetings generated by both Java and native code, with performance metrics for comparison.

• simple-jni: Main Android application module that demonstrates JNI functionality with a Jetpack Compose UI

• jnihellostachka: JNI implementation using a custom JNI generator
• hellostachka-lib: Native library built with Bazel, demonstrating external build system integration

• jnigenerator: Custom JNI generator tools
  • python: Python scripts for JNI code generation
  • cpp: C++ essential headers and implementations for JNI
  • java/annotations: Java annotations for JNI generation

• libloader: Utility module for loading native libraries with performance tracking
• logging: Simple logging utilities
• theme: UI theme components
• icons: Application icons

• buildSrc: Custom Gradle build logic including JNI build configuration
• external-build-plugin: Gradle plugin for integrating with external build systems (Bazel)

The project supports three different native build approaches, configurable via the jniBuild property in local.properties:

jniBuild=cmake

Uses CMake to build the native code. This is the most modern approach for native builds in Android.

jniBuild=ndkBuild

Uses the older ndk-build system with Android.mk files.

jniBuild=externalBuild

Uses Bazel as an external build system. The native code is defined in the hellostachka-lib directory.

Known Issue: Currently, libraries built with Bazel only work on Android SDK 28.

The project demonstrates two different approaches to JNI:

1. Standard JNI (HelloStachka.kt):

   • Traditional JNI approach with manually created header files
   • Native implementation in hellostachka-lib/cpp/hello_stachka.cpp

2. JNI Generator (JniHelloStachka.java):

   • Uses custom annotations and JNI generator
   • Simplifies JNI development by automating header generation
   • Native implementation in jnihellostachka/src/main/cpp/jni_hello_stachka.cpp

Both implementations provide a sayHello method that returns a greeting string from native code.

The project uses a custom LibLoader utility that:

• Loads native libraries
• Measures and records loading time
• Provides an observer pattern to notify components when libraries are loaded

The UI is built with Jetpack Compose and features:

• Material 3 design components
• Animated transitions
• Performance measurement for both Java and native method calls
• Display of loaded native libraries with loading times

1. Clone the repository

2. Configure your preferred JNI build system in local.properties:

   jniBuild=cmake  # or ndkBuild or externalBuild

3. For External ensure Bazel is installed on your system

4. Build and run the project using Android Studio or Gradle:

   ./gradlew :simple-jni:assembleDebug
   

• Android External Native Builds
• Android NDK Samples
• Bazel Build System