JNI Callback

Callback.java

interface CallbackInterface {
	public void callback();
}

public class Callback {

	static native void nativeCallJavaMethod(CallbackInterface cb);

	public static void main(String []args) {
		System.loadLibrary("callback");

		/* Passing code as argument */
		nativeCallJavaMethod(new CallbackInterface() {
			public void callback() {
				System.out.println("Hello from CallbackInterface");
			}
		});
	}
}

libcallback.c

#include "Callback.h"

JNIEXPORT void JNICALL Java_Callback_nativeCallJavaMethod
(JNIEnv *env, jclass cls, jobject impl_obj) 
{
	jclass impl_cls;
	jmethodID impl_cb_mid;

	impl_cls = (*env)->GetObjectClass(env, impl_obj);
	if (!impl_cls)
		return;
	
	impl_cb_mid = (*env)->GetMethodID(env, impl_cls, "callback", "()V"); 
	if (!impl_cb_mid)
		return;

	(*env)->CallVoidMethod(env, impl_obj, impl_cb_mid);
}

Makefile

JAVA_HOME := /usr/lib/jvm/java-8-openjdk-amd64
CFLAGS += -I$(JAVA_HOME)/include -I$(JAVA_HOME)/include/linux

all: libcallback.so

libcallback.so: libcallback.c Callback.h 
Callback.h: Callback.class
Callback.class: Callback.java

%.class: %.java
	javac $<

%.h: %.class
	javah $(<:.class=)

%.so: %.c
	$(CC) $(CFLAGS) $(LDFLAGS) -fPIC -shared -o $@ $^