package org.stackoverflow.data;

public class BeanObject {

    String foo = "";

    public String getFoo() {

        return foo;
    }
}

package org.stackoverflow.jni;

import org.stackoverflow.data.BeanObject;

public class NativeClazz {

    // Static area for forced initialization
    static {

        // Load Native Library (C++)
        System.loadLibrary("Native_Library_File_Name");

        // Load Class and Method Ids
        initialize();
    }

    /**
     * Native Initialization loads ClassIDs and MethodIDs to static variables.
     */
    public static native void initialize();

    /**
     * Native Destructor unloads ClassIDs from global memory.
     */
    public static native void destroy();

    /**
     * A static native method you plan to call.
     */
    public static native void staticNativeMethod(BeanObject bean);

    /**
     * A non-static native method you plan to call, to show this also works with
     * instantiated Java classes.
     */
    public native void instanceNativeMethod(BeanObject bean);
}

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class org_stackoverflow_jni_NativeClazz */

#ifndef _Included_org_stackoverflow_jni_NativeClazz
#define _Included_org_stackoverflow_jni_NativeClazz
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     org_stackoverflow_jni_NativeClazz
 * Method:    initialize
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_initialize
  (JNIEnv *, jclass);

/*
 * Class:     org_stackoverflow_jni_NativeClazz
 * Method:    destroy
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_destroy
  (JNIEnv *, jclass);

/*
 * Class:     org_stackoverflow_jni_NativeClazz_staticNativeMethod
 * Method:    staticNativeMethod
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_staticNativeMethod
  (JNIEnv *, jclass, jobject);

/*
 * Class:     org_stackoverflow_jni_NativeClazz_instanceNativeMethod
 * Method:    instanceNativeMethod
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_instanceNativeMethod
  (JNIEnv *, jobject, jobject);

#ifdef __cplusplus
}
#endif
#endif

#include "org_stackoverflow_jni_NativeClazz.h"

using namespace std;

/**************************************************************
 * Static Global Variables to cache Java Class and Method IDs
 **************************************************************/
static jclass JC_BeanObject;
static jmethodID JMID_BeanObject_getFoo;

/**************************************************************
 * Initialize the static Class and Method Id variables
 **************************************************************/
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_initialize
        (JNIEnv * env, jclass clazz) {

    // Temporary local reference holder
    jclass tempLocalClassRef;

    // STEP 1/3 : Load the class id
    tempLocalClassRef = env->FindClass("org/stackoverflow/data/BeanObject");

    // STEP 2/3 : Assign the ClassId as a Global Reference
    JC_BeanObject = (jclass) env->NewGlobalRef(tempLocalClassRef);

    // STEP 3/3 : Delete the no longer needed local reference
    env->DeleteLocalRef(tempLocalClassRef);

    // Load the method id
    JMID_BeanObject_getFoo = env->GetMethodID(JC_BeanObject, "getFoo", "(Ljava/lang/String;)V");

    // ... repeat prior line for any other methods of BeanObject

    // ... repeat STEPS 1-3 for any other classes; re-use tempLocalClassRef.
}

/**************************************************************
 * Destroy the global static Class Id variables
 **************************************************************/
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_destroy
        (JNIEnv * env, jclass clazz) {

    // Destroy the global references
    env->DeleteGlobalRef(JC_BeanObject);

    // ... repeat for any other global references

}

/**************************************************************
 * A Static Native Method
 **************************************************************/
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_staticNativeMethod
               (JNIEnv * env, jclass clazz, jobject jBeanObject) {

    jstring jFoo = (jstring)env->CallObjectMethod(jBeanObject, JMID_BeanObject_getFoo);
}

/**************************************************************
 * Instance / Non-Static Native Method
 **************************************************************/
JNIEXPORT void JNICALL Java_org_stackoverflow_jni_NativeClazz_instanceNativeMethod
               (JNIEnv * env, jobject selfReference, jobject jBeanObject) {

    jstring jFoo = (jstring)env->CallObjectMethod(jBeanObject, JMID_BeanObject_getFoo);
}

public class SimpleClazz {

    public int value = 10;

    public native int getValue();

    static {
        // Load Native Library
        System.loadLibrary("The native library name");
    }
}

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class SimpleClazz */

#ifndef _Included_SimpleClazz
#define _Included_SimpleClazz
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     SimpleClazz
 * Method:    getValue
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_SimpleClazz_getValue
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

#include <jni.h>
#include <SimpleClazz.h>

static jclass simpleCls;

// According to http://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/invocation.html#JNI_OnLoad
// The VM calls JNI_OnLoad when the native library is loaded (for example, through System.loadLibrary).
jint JNI_OnLoad(JavaVM* vm, void* reserved) {
    if ((*vm)->GetEnv(vm, (void **) &env, JNI_VERSION_1_6) != JNI_OK) {
        return JNI_ERR;
    } else {
        jclass localSimpleCls = (*env)->FindClass("SimpleClazz");

        if (localSimpleCls == NULL) {
            return JNI_ERR;
        }
        simpleCls = (jclass) (*env)->NewGlobalRef(env, localSimpleCls);
    }
    return JNI_VERSION_1_6;
}



JNIEXPORT jint JNICALL Java_SimpleClazz_getValue(JNIEnv * env, jobject thiz){
    static jfieldID valueID = NULL;
    if (valueID == NULL) {
        valueID = (*env)->GetFieldID(env, simpleCls, "value", "I");
        if (valueID == NULL){
            return JNI_ERR;         // Exception thrown
        }
    }
    jint value = (*env)->GetIntField(env, thiz, valueID);
    return value;
}

// According to http://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/invocation.html#JNI_OnUnload
// The VM calls JNI_OnUnload when the class loader containing the native library is garbage collected.
void JNI_OnUnload(JavaVM *vm, void *reserved) {
    JNIEnv* env;
    if ((*vm)->GetEnv(vm, (void **) &env, JNI_VERSION_1_6) != JNI_OK) {
        // Something is wrong but nothing we can do about this :(
        return;
    } else {
        if (0 != NULL){
            (*env)->DeleteGlobalRef(env, simpleCls);
        }
    }
}

typedef struct MYVARIANT_FID_CACHE {
    int cached;
    jclass clazz;
    jfieldID pAddress;
} MYVARIANT_FID_CACHE;

MYVARIANT_FID_CACHE VARIANTFc;

void cacheMYVARIANTFields(JNIEnv *env, jobject lpObject)
{
    if (VARIANTFc.cached) return;
    VARIANTFc.clazz = env->GetObjectClass(lpObject);
    VARIANTFc.pAddress = env->GetFieldID(VARIANTFc.clazz, "pAddress", "I");
    VARIANTFc.cached = 1;
}

VARIANT *getMYVARIANTFields(JNIEnv *env, jobject lpObject, VARIANT *lpStruct)
{
    if (!VARIANTFc.cached) cacheVARIANT2Fields(env, lpObject);

    lpStruct = (VARIANT*)(env->GetIntField(lpObject, VARIANTFc.pAddress));

    return lpStruct;
}

package demo;
public class WithNatives {

 static {
   initIDs();
 }

 private static native void initIDs();

}

static jmethodID methodId;

void JNICALL Java_demo_WithNatives_initIDs(JNIEnv *env, jclass clazz)
{
   // initialize methodId
}