Summary

In this chapter we introduce you to the JNI, a standard API available on Java to interact with native code written in Assembly, C or C++ that it is available to any Android Developer with the Android NDK kit installed.

In the first section we explain how to setup a project with JNI code on Android Studio and how to call C function and C++ member functions from any Java class on your application.

Later, we use the JNI interface to execute a Loader asynchronous background work on a native function. The native function was able to convert a colorful image to a gray image on a Java background thread created by the AsyncTaskLoader.

Next, we discover how to attach and detach a pure native thread created using the C++ standard library to the JVM. The attached thread worked as a normal Java thread and managed its own JNI Environment, resources and references.

In the meantime, we also discovered the differences between JNI global and Local references and how to access a Java object field from...