Java類：UserInfo

public class UserInfo {
	static {
		System.loadLibrary("userinfo");
	}
	// 從JNI中直接訪問欄位
	public String mUserName;
	public int mUserAge;
	public long mMoney;
	
	public UserInfo() {
		
	}
	
	public int getUserAge() {
		return mUserAge;
	}
	
	public native void setUserName(String name);
	public native void setUserAge(int age);
	public native void setUserMoney(long money);
}
 

1、FindClass：找到某個類，並返回jclass物件

2、GetObjectClass: 獲取到某個物件的型別，並返回jclass物件

3、GetFieldID：獲取到欄位的ID

4、SetIntField/SetLongField/SetObjectField：為欄位設值

基於上面的幾個方法，可以編寫程式碼如下：

/*
 * Class:     com_iflytek_testjni_UserInfo
 * Method:    setUserName
 * Signature: (Ljava/lang/String;)V
 */
JNIEXPORT void JNICALL Java_com_iflytek_testjni_UserInfo_setUserName(JNIEnv *env, jobject obj, jstring jstr) {
	jfieldID fid;

	jclass cls = (*env)->GetObjectClass(env, obj);
	fid = (*env)->GetFieldID(env, cls, "mUserName", "Ljava/lang/String;");
	(*env)->SetObjectField(env, obj, fid, jstr);
}

/*
 * Class:     com_iflytek_testjni_UserInfo
 * Method:    setUserAge
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_com_iflytek_testjni_UserInfo_setUserAge(JNIEnv *env, jobject obj, jint age) {
	jclass objClass = (*env)->FindClass(env, "com/iflytek/testjni/UserInfo");
	jfieldID ageID = (*env)->GetFieldID(env, objClass, "mUserAge", "I");
	(*env)->SetIntField(env, obj, ageID, (int)age);
}

/*
 * Class:     com_iflytek_testjni_UserInfo
 * Method:    setUserMoney
 * Signature: (J)V
 */
JNIEXPORT void JNICALL Java_com_iflytek_testjni_UserInfo_setUserMoney(JNIEnv *env, jobject obj, jlong money) {
	jclass objClass = (*env)->FindClass(env, "com/iflytek/testjni/UserInfo");
	jfieldID id = (*env)->GetFieldID(env, objClass, "mMoney", "J");
	(*env)->SetLongField(env, obj, id, (long)money);
}
 

注意：由於方法簽名、欄位名稱都是寫死在C語言中的，因此程式碼不能混淆。