Retrieve the Java instance of the Android activity class.
Returns the jobject representing the instance of the Activity class of the Android application, or NULL on error.
The prototype of the function in SDL's code actually declares a void* return type, even if the implementation returns a jobject. The rationale being that the SDL headers can avoid including jni.h.
The jobject returned by the function is a local reference and must be released by the caller. See the PushLocalFrame() and PopLocalFrame() or DeleteLocalRef() functions of the Java native interface:
https://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html
This function is available since SDL 2.0.0.