Java JNI入门篇——C++访问并修改Java中的变量

这里不在重复Java JNI 的开发过程了，不熟悉的同学请参考：Java JNI HelloWorld
直接上主要代码：

VarJNI.java

package com.example.jni;public class VarJNI {    static {        System.loadLibrary("varjni");    }    private int number = 9;    private String content = "I'm from Java!";    public native void changeValue();    public static void main(String[] args) throws Exception {        VarJNI item = new VarJNI();        System.out.println("before call number: " + item.number);        System.out.println("before call content: " + item.content);        item.changeValue();        System.out.println("after call number: " + item.number);        System.out.println("after call content: " + item.content);    }}

varjni.cpp

// varjni.cpp : Defines the exported functions for the DLL application.//#include "stdafx.h"#include "com_example_jni_VarJNI.h"#include <iostream>#include <math.h>/** Class:     com_example_jni_VarJNI* Method:    changeValue* Signature: ()V*/JNIEXPORT void JNICALL Java_com_example_jni_VarJNI_changeValue(JNIEnv * env, jobject obj) {    jclass clazz = env->GetObjectClass(obj);    jfieldID int_fieldID = env->GetFieldID(clazz, "number", "I");    jint number = env->GetIntField(obj, int_fieldID);    //change number value    number = (int)pow(number, 2);    env->SetIntField(obj, int_fieldID, number);    //be careful Ljava/lang/String    jfieldID string_fieldID = env->GetFieldID(clazz, "content", "Ljava/lang/String;");    jstring content = (jstring)env->GetObjectField(obj, string_fieldID);    const char* cc = env->GetStringUTFChars(content, 0);    env->ReleaseStringUTFChars(content, cc);    char hello[] = "I'm from C++!\n";    jstring jhello = env->NewStringUTF(hello);    //change content value    env->SetObjectField(obj, string_fieldID, jhello);    return;}

ok!