第一步：编写Java端代码

定义一个Java类

public class TestNativeDemo {
 
    // 声明本地方法
    public native String testJni(String arg);
 
    static {
        // 加载DLL文件
        System.loadLibrary("TestNativeDemoCPP");
    }
 
    public static void main(String args[]) {
        TestNativeDemo ob = new TestNativeDemo();
        // 调用本地方法
        String result = ob.testJni("Hello,Jni"); // call a native method
        System.out.println("TestNativeDemo.testJni=" + result);
    }
}

编译之后在生成TestNativeDemo.class的bin目录下执行javah TestNativeDemo命令生成头文件TestNativeDemo.h

----------------------------------------------

/* DO NOT EDIT THIS FILE - it is machine generated */sky7034
#include <jni.h>
/* Header for class TestNativeDemo */
 
 
#ifndef _Included_TestNativeDemo //避免重复包含头文件  
#define _Included_TestNativeDemo
#ifdef __cplusplus //c++编译环境中才会定义__cplusplus  
extern "C" { //告诉编译器下面的函数是c语言函数（因为c++和c语言对函数的编译转换不一样，主要是c++中存在重载）   
 
#endif
/*
 * Class:     TestNativeDemo
 * Method:    testJni
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_TestNativeDemo_testJni
  (JNIEnv *, jobject, jstring);
 
#ifdef __cplusplus
}
#endif
#endif