jni doc

#include <jni.h>
#include <stdio.h>
#include "TestJNIString.h"
 
JNIEXPORT jstring JNICALL Java_TestJNIString_sayHello(JNIEnv *env, jobject thisObj, jstring inJNIStr) {
   // Step 1: Convert the JNI String (jstring) into C-String (char*)
   const char *inCStr = (*env)->GetStringUTFChars(env, inJNIStr, NULL);
   if (NULL == inCSt) return NULL;
 
   // Step 2: Perform its intended operations
   printf("In C, the received string is: %s\n", inCStr);
   (*env)->ReleaseStringUTFChars(env, inJNIStr, inCStr);  // release resources
 
   // Prompt user for a C-string
   char outCStr[128];
   printf("Enter a String: ");
   scanf("%s", outCStr);    // not more than 127 characters
 
   // Step 3: Convert the C-string (char*) into JNI String (jstring) and return
   return (*env)->NewStringUTF(env, outCStr);
}

Ref : https://www3.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html