c++ - Java 使用 JNI : why does the JNIEnv pointer get dereferenced twice? 调用 C++

Question

此代码直接复制自http://java.sun.com/docs/books/jni/html/objtypes.html#4013

JNIEXPORT jstring JNICALL 
Java_Prompt_getLine(JNIEnv *env, jobject obj, jstring prompt)
{
    char buf[128];
    const jbyte *str;
    str = (*env)->GetStringUTFChars(env, prompt, NULL);
    if (str == NULL) {
         return NULL; /* OutOfMemoryError already thrown */
    }
     printf("%s", str);
    (*env)->ReleaseStringUTFChars(env, prompt, str);
    /* We assume here that the user does not type more than
     * 127 characters */
    scanf("%s", buf);
    return (*env)->NewStringUTF(env, buf);
}

为什么都不是

env->GetStringUTFChars(...

也不

(*env).GetStringUTFChars(...

?

Answer 1

来自 earlier在您在问题中链接的文档中:

The first parameter, the JNIEnv interface pointer, points to a location that contains a pointer to a function table

阅读本文似乎 JNIEnv 本身就是一个指针。它甚至是描述段落下方关系的漂亮图片。