NativeDemo.c

#include<jni.h>
#include<stdio.h>
#include "NativeDemo.h"

JNIEXPORT void JNICALL Java_NativeDemo_test(JNIEnv *env, jobject obj){

	jclass cls;
	jfieldID fid;
	jint i;
	
	printf("Inside native method.");
	
	cls = (*env) ->GetObjectClass(env, obj);
	fid = (*env) ->GetFieldID(env, cls, "i", "I");
	
	if(fid == 0){
		printf("Could not get field ID.");
		return;
	}
	i=(*env)->GetIntField(env, obj, fid);
	printf("i = %d\n", i);
	(*env)->SetIntField(env, obj, fid, 2*i);
	printf("Ending of native method.");
	// function body
	printf("Hello world");
}