General notes on JNI

Method invocations are synchronous:

• Java to C

• C to Java

The JNIEnv pointer is only valid in the current thread - do not attempt to pass the pointer to other threads.

JNI does not check against NULL parameters.

The set of arguments for native methods follow these requirements:

• the first argument is always the JNIEnv pointer

• if the method is nonstatic, the second argument is a jobject representing the invoking object "this"

• the remaining arguments come from the method aignature in Java, typed with their JNI counterpart

As C does not support overloading, Java overloaded methods are appended with two underscores followed by the argument signature (so to avoid name clash)

JNI resolves native methods in the following order:

1. first the short name

2. then the long name, i.e. with the argument signature

Overview of JNI

1. Declare methods in Java with the "native" keyword

2. Invoke JavaH to generate the corresponding C header

3. Include the header do a C source file and implement the declared functions, paying attention to cast types, unwrap objects and modify fields.