Use jni to directly access fields in java objects

Java class: UserInfo

Public class UserInfo {static {System. loadLibrary ("userinfo");} // directly access the public String mUserName; public int mUserAge; public long mMoney; public UserInfo () {} public int getUserAge () field from JNI () {return mUserAge;} public native void setUserName (String name); public native void setUserAge (int age); public native void setUserMoney (long money );}

Three of the setting methods are expected to be implemented using C. Several Functions in JNI are involved here:

1. FindClass: locate a class and return the jclass object.

2. GetObjectClass: gets the type of an object and returns the jclass object.

3. GetFieldID: obtains the field ID.

4. SetIntField/SetLongField/SetObjectField: Set the field value.

Based on the above methods, you can write the code as follows:

/* * 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);}

Compile Android. mk and pass the test.

Note: Because the method signature and field names are all written in the C language, the Code cannot be confused.