2.5.md

public class JNIReference extends BaseOperation {


    @Override
    public void invoke() {
//        errorCacheLocalReference();
//        cacheWithGlobalReference();
//        useWeakGlobalReference();
        print( errorCacheLocalReference(), cacheWithGlobalReference(), useWeakGlobalReference());

    }

    public native String errorCacheLocalReference();
    public native String cacheWithGlobalReference();
    public native String useWeakGlobalReference();
}

/**
 * 局部引用
 */
extern "C"
JNIEXPORT jstring JNICALL
Java_com_jdqm_ndktutorials_jni_JNIReference_errorCacheLocalReference(JNIEnv *env, jobject thiz) {
    jclass localRefs = env->FindClass("java/lang/String");
    jmethodID mid = env->GetMethodID(localRefs, "<init>", "(Ljava/lang/String;)V");
    jstring str = env->NewStringUTF("string");
    //局部引用如果引用过多需要手动及时释放
    for (int i = 0; i < 1000; ++i) {
        jclass cls = env->FindClass("java/lang/String");

        env->DeleteLocalRef(cls);

    }
    return static_cast<jstring>(env->NewObject(localRefs, mid, str));
}

/**
 * 全局引用
 * 可以全局缓存
 */
extern "C"
JNIEXPORT jstring JNICALL
Java_com_jdqm_ndktutorials_jni_JNIReference_cacheWithGlobalReference(JNIEnv *env, jobject thiz) {
    static jclass stringClass = nullptr;
    if (stringClass == nullptr) {
        jclass cls = env->FindClass("java/lang/String");
        stringClass = static_cast<jclass>(env->NewGlobalRef(cls));
        env->DeleteLocalRef(cls);
    } else {
        LOGD("USER CACHED");
    }
    jmethodID mid = env->GetMethodID(stringClass, "<init>", "(Ljava/lang/String;)V");
    jstring str = env->NewStringUTF("string");
    return static_cast<jstring>(env->NewObject(stringClass, mid, str));
}

/**
 * 弱引用
 */
extern "C"
JNIEXPORT jstring JNICALL
Java_com_jdqm_ndktutorials_jni_JNIReference_useWeakGlobalReference(JNIEnv *env, jobject thiz) {

    static jclass stringClass = nullptr;
    if (stringClass == nullptr) {
        jclass cls = env->FindClass("java/lang/String");
        stringClass = static_cast<jclass>(env->NewWeakGlobalRef(cls));
        env->DeleteLocalRef(cls);
    } else {
        LOGD("USER CACHED");
    }
    jmethodID mid = env->GetMethodID(stringClass, "<init>", "(Ljava/lang/String;)V");
    jboolean isGc = env->IsSameObject(stringClass, nullptr);
    if (!isGc) {
        jstring str = env->NewStringUTF("string");
        return static_cast<jstring>(env->NewObject(stringClass, mid, str));
    } else {
        jstring str = env->NewStringUTF("弱引用被释放");
        return static_cast<jstring>(env->NewObject(stringClass, mid, str));
    }
}