如何使用JNI创建本机类？

Question

I want to create C++ class with constructor and one method which returns string. My question is: how to initialize object of type "native class" in Java using C++ constructor and then from this Java object call native method?

Answer 1

There is no 'native class' in Java; we have 'native methods' that can be part of any Java class. The native methods are implemented as extern "C" functions.

In the nutshell, you can create in your Java two native methods, eg createNativeInstance and getNativeString . Note that you probably need another method to release the native instance:

#include <jni.h>

JNIEXPORT
jlong Java_test_createNativeInstance(JNIEnv *, jobject ) {
    return reinterpret_cast<jlong>(new CppClass());
}

JNIEXPORT
jstring Java_test_getNativeString(JNIEnv *env, jobject obj, jlong cppClassPtr) {
    CppClass* pCppClass = reinterpret_cast<CppClass*>(cppClassPtr);
    return env->NewStringUTF(env, pCppClass->getString();
}

JNIEXPORT
void Java_test_releaseNativeInstance(JNIEnv *env, jobject obj, jlong cppClassPtr) {
    CppClass* pCppClass = reinterpret_cast<CppClass*>(cppClassPtr);
    delete pCppClass;
}