instancefieldaccess.c

jni java本地接口编程例子原代码,是java调用本地操作系统代码的接口

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

JNIEXPORT void JNICALL 
Java_InstanceFieldAccess_accessField(JNIEnv *env, jobject obj)
{
    jfieldID fid;   /* store the field ID */
    jstring jstr;
    const char *str;

    /* Get a reference to obj苨 class */
    jclass cls = (*env)->GetObjectClass(env, obj);

    printf("In C:\n");

    /* Look for the instance field s in cls */
    fid = (*env)->GetFieldID(env, cls, "s",
                             "Ljava/lang/String;");
    if (fid == NULL) {
        return; /* failed to find the field */
    }

    /* Read the instance field s */
    jstr = (*env)->GetObjectField(env, obj, fid);
    str = (*env)->GetStringUTFChars(env, jstr, 0);
    if (str == NULL) {
        return; /* out of memory */
    }
    printf("  c.s = \"%s\"\n", str);
    (*env)->ReleaseStringUTFChars(env, jstr, str);

    /* Create a new string and overwrite the instance field */
    jstr = (*env)->NewStringUTF(env, "123");
    (*env)->SetObjectField(env, obj, fid, jstr);
}