C 调Java 与 Java 调C 过程其它的基本一致 只是native 方法上有差不，这里通过几个例子来说明，1.回调一般方法(无参无返回) 2.回调带int 参数方法 3.回调带String 参数方法

native 方法实现

#include "com_atguigu_ccalljava_JNI.h"
#include <stdlib.h>
#include <stdio.h>

#include <android/log.h>
#define LOG_TAG "System.out"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)



/**
 * 让C代码调用 java 中JNI类的 public int add(int x, int y)
 */
JNIEXPORT void JNICALL Java_com_atguigu_ccalljava_JNI_callbackAdd
(JNIEnv * env, jobject jobj){

    //1.得到字节码
    //jclass      (*FindClass)(JNIEnv*, const char*);
    jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/JNI");
    //2.得到方法
    //jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
    //最后一个参数是方法签名
    jmethodID jmethodIDs= (*env)->GetMethodID(env,jclazz,"add","(II)I");
    //3.实例化该类
    // jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject  jobject =(*env)->AllocObject(env,jclazz);
    //4.调用方法
    //jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);
    jint value =  (*env)->CallIntMethod(env,jobject,jmethodIDs,99,1);
    //成功调用了public int add(int x, int y)
    printf("value===%d\n",value);
    LOGE("value===%d\n",value);

};

/**
 * 让C代码调用
     * public void helloFromJava()
 */
JNIEXPORT void JNICALL Java_com_atguigu_ccalljava_JNI_callbackHelloFromJava
        (JNIEnv * env, jobject jobj){
    //1.得到字节码
    //jclass      (*FindClass)(JNIEnv*, const char*);
    jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/JNI");
    //2.得到方法
    //jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
    //最后一个参数是方法签名
    jmethodID jmethodIDs= (*env)->GetMethodID(env,jclazz,"helloFromJava","()V");
    //3.实例化该类
    // jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject  jobject =(*env)->AllocObject(env,jclazz);
    //4.调用方法
    //void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
     (*env)->CallVoidMethod(env,jobject,jmethodIDs);
    //成功调用了public void helloFromJava()

};

/**
 * 让C代码调用void printString(String s)
 */
JNIEXPORT void JNICALL Java_com_atguigu_ccalljava_JNI_callbackPrintString
        (JNIEnv * env, jobject job){
    //1.得到字节码
    //jclass      (*FindClass)(JNIEnv*, const char*);
    jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/JNI");
    //2.得到方法
    //jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
    //最后一个参数是方法签名
    jmethodID jmethodIDs= (*env)->GetMethodID(env,jclazz,"printString","(Ljava/lang/String;)V");
    //3.实例化该类
    // jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject  jobject =(*env)->AllocObject(env,jclazz);
    //4.调用方法
    //void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
    //jstring     (*NewStringUTF)(JNIEnv*, const char*);
    jstring jst = (*env)->NewStringUTF(env,"I am afu!!!(*env)->");
    (*env)->CallVoidMethod(env,jobject,jmethodIDs,jst);
    //成功调用了public void helloFromJava()
};

/**
 * 让C代码静态方法 static void sayHello(String s)
 */
JNIEXPORT void JNICALL Java_com_atguigu_ccalljava_JNI_callbackSayHello
        (JNIEnv * env, jobject jobj){

    //1.得到字节码
    //jclass      (*FindClass)(JNIEnv*, const char*);
    jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/JNI");
    //2.得到方法
    //jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);
    //最后一个参数是方法签名
    jmethodID jmethodIDs= (*env)->GetStaticMethodID(env,jclazz,"sayHello","(Ljava/lang/String;)V");
    //3.实例化该类
    //void        (*CallStaticVoidMethod)(JNIEnv*, jclass, jmethodID, ...);
    jstring jst = (*env)->NewStringUTF(env,"I am android1223");
    (*env)->CallStaticVoidMethod(env,jclazz,jmethodIDs,jst);
    //成功调用了static void sayHello(String s)

}


/**
 * instance:谁调用了当前Java_com_atguigu_ccalljava_JNI_callBackShowToast对应的Java的接口
 * 就是谁的实例：当前是JNI.this-->MainActivity.this
 */
 void Java_com_atguigu_ccalljava_JNI_callBackShowToast(JNIEnv *env, jobject instance) {

    //1.得到字节码
    //jclass      (*FindClass)(JNIEnv*, const char*);
    jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/MainActivity");
    //2.得到方法
    //最后一个参数是方法签名
    //jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
    jmethodID jmethodIDs= (*env)->GetMethodID(env,jclazz,"showToast","()V");
    //3.实例化该类
    //   jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject  jobject1 = (*env)->AllocObject(env,jclazz);
    //4.调用方法
    //void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
    (*env)->CallVoidMethod(env,jobject1,jmethodIDs);
    //成功调用了static void sayHello(String s)

}

 void Java_com_atguigu_ccalljava_MainActivity_callBackShowToast(JNIEnv *env, jobject instance) {

     //1.得到字节码
     //jclass      (*FindClass)(JNIEnv*, const char*);
     jclass jclazz = (*env)->FindClass(env,"com/atguigu/ccalljava/MainActivity");
     //2.得到方法
     //最后一个参数是方法签名
     //jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
     jmethodID jmethodIDs= (*env)->GetMethodID(env,jclazz,"showToast","()V");
     //3.实例化该类
     //   jobject     (*AllocObject)(JNIEnv*, jclass);
     //jobject  jobject1 = (*env)->AllocObject(env,jclazz);
     //4.调用方法
     //void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
     (*env)->CallVoidMethod(env,instance,jmethodIDs);
     //成功调用了static void sayHello(String s)
}