Architecture Notes

Attaching JNI to your code

The existence of JNI in your code must be isolated and self-contained (best practice: low coupling):

• a set of Java classes dealing with JNI-related issues (e.g. declaring the Java native methods)

• a set of C source files dealing with JNI-related issues (e.g. converting between JNI and C types and modifying Java object fields

Interfacing to the native code

Having an API header in your library is important

Reuse and low coupling: library can be easily attached:

• to JNI and then be called by Java

• to other native applications

• to a standalone piece of native code and then be called directly from C/C++

Performance

Avoid the overhead introduced by JNI to the communication between the JVM and native codes:

• perform a full computation on one side and then transmit the result to the other; do not perform in pieces and transmit in pieces unless necessary

• retrieve and modify JNI arrays by range, not element by element

• look-ups for method and field IDs are very costly