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

JNIEXPORT void JNICALL
Java_HelloWorld_print(JNIEnv *env, jobject obj)
{
  jstring Unicode_str;
  const jbyte *UTF_str;
  jclass class;
  jmethodID method_id;
  jobject this_thread;

  fprintf(stderr,"Starting Java_HelloWorld_print\n");

  /*
    In C++ the following call would have been written:

    class = env->FindClass("java/lang/Thread");
  */
  class = (*env)->FindClass(env, "java/lang/Thread");
  if (NULL == class) {
    fprintf(stderr,"Could not find class java.lang.Thread\n");
    return;
  }

  method_id = (*env)->GetStaticMethodID(env, class,
    "currentThread", "()Ljava/lang/Thread;");
  if (NULL == method_id) {
    fprintf(stderr,
      "Could not find static method currentThread of java.lang.Thread\n");
    return;
  }

  this_thread = (*env)->CallStaticObjectMethod(env, class, method_id);
  if (NULL == this_thread) {
    fprintf(stderr,"Could not get the currentThread\n");
    return;
  }

  class = (*env)->GetObjectClass(env, this_thread);
  if (NULL == class) {
    fprintf(stderr,"Could not find class java.lang.Thread\n");
    return;
  }

  method_id = (*env)->GetMethodID(env, class,
    "toString", "()Ljava/lang/String;");
  if (NULL == method_id) {
    fprintf(stderr,"Could not find method toString of java.lang.Thread\n");
    return;
  }

  Unicode_str = (*env)->CallObjectMethod(env, this_thread, method_id);
  if (NULL == Unicode_str) {
    fprintf(stderr,"Did not get the name of the current thread\n");
    return;
  }

  UTF_str = (*env)->GetStringUTFChars(env, Unicode_str, NULL);
  if (NULL == UTF_str) {
    return;                     /* OutOfMemoryError already thrown */
  }

  /*
   * Here I *KNOW* that the UTF string returned contains only 7-bit ASCII
   * characters, that's why I'm passing it to printf.
   *
   * When this is *not* the case, see section 8.2 of the JNI Guide...
   */
  printf("Thread \"%s\" says using JNI: Hello World!\n", UTF_str);

  /* Collecting our garbage to avoid a memory leak */
  (*env)->ReleaseStringUTFChars(env, Unicode_str, UTF_str);
  return;
}