Hello JNI

Demo Android app that shows JNI end to end: a native C library (libhello-jni.so) built for all common ABIs, Java calling into native code, and a small crackme-style check.

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Features

• JNI — getHelloString() returns a string from native code; checkActivation() validates input in C.
• Native — CMake-built shared library, C (not C++), armeabi-v7a, arm64-v8a, x86, x86_64.
• Crackme-style check — single-byte XOR compare against an embedded table (educational / demo).

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Requirements

• Android Studio Koala+ or compatible, JDK 17+ (as required by AGP 9).
• Android SDK with API 36 and NDK + CMake (install via SDK Manager).

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Build

./gradlew assembleDebug

Debug APK: app/build/outputs/apk/debug/app-debug.apk

Release (after you configure signing):

./gradlew assembleRelease

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Project layout

Path	Purpose
app/src/main/java/.../MainActivity.java	JNI declarations, System.loadLibrary, UI logic
app/src/main/cpp/native-lib.c	Native implementation + XOR check
app/src/main/cpp/CMakeLists.txt	Native build
app/src/main/res/	Layouts, themes, drawables

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License

This project is licensed under the MIT License — see LICENSE.