Document the reason for using RegisterNatives.

Author: DanAlbert

README.md

@@ -43,6 +43,45 @@ typical applications that need to use some C++ via JNI. The "Game Activity"
 template is a good starting point for game-like apps (that is, apps that do not
 use the Android UI, but instead render their own UI using OpenGL or Vulkan).
 
+## Best practices shown here
+
+There are a few best practices shown throughout this repository that should be
+explained, but there's no central place to discuss those in the code, so we'll
+discuss those here.
+
+### `RegisterNatives`
+
+We prefer using `RegisterNatives` via `JNI_OnLoad` over the name-based matching
+that Studio's New Project Wizard will typically create, e.g. JNI functions that
+follow the pattern `JNIEXPORT void JNICALL Java_com_etc_ClassName_methodName`.
+That approach to matching C/C++ functions to their Java `native` function (or
+Kotlin `external fun`) makes for a shorter demo when there are only a small
+number of functions, but it has a number of disadvantages:
+
+1. Mistakes are uncovered late. An incorrectly named function will not cause an
+   error until called by Java, so it's easier to ship bugs if your testing does
+   not cover all JNI methods.
+2. All JNI symbols must be exported, leading to more relocations, larger
+   binaries, and less effective link-time optimization (LTO).
+3. The first call to a JNI function will be slower than subsequent calls, as the
+   Java call will first need to find a matching implementation.
+4. If you want to rename the function in Java, you have to also rename the C/C++
+   function.
+
+Instead, most apps should use `RegisterNatives` via `JNI_OnLoad`. This performs
+up-front registration of native methods with an explicit mapping. It takes a
+little bit more up-front-work, but doing so counters all of the disadvantages
+above:
+
+1. Mistakes are caught early. An incorrectly named function will cause an error
+   during library load.
+2. The only symbol that typically must be exported is `JNI_OnLoad`. Some use
+   cases may additionally need `ANativeActivty_OnCreate` or similar.
+3. No lookup required for the first call to each native function, so performance
+   overhead is consistent.
+4. The Java or C/C++ functions can be renamed at will, and only the map needs to
+   be updated to match.
+
 ## Additional documentation
 
 - [Add Native Code to Your Project](https://developer.android.com/studio/projects/add-native-code.html)