package zq.ndkdemo;

public class NDKTools {

    static {
        System.loadLibrary("ndkdemomk-jni");//这里的"ndkdemomk-jni"是下面.mk文件里局部模块的值,这个到后面我会解释
    }

    public static native String getNDKcontent();//您在Java里调用so库的静态方法
}

javah -o ndkdemoHFile.h -jni -classpath ./main/java/  zq.ndkdemo.NDKTools
javah -o 你要打包的.h文件名加后缀 -jni -classpath 中间的路径  app包名+工具类名

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class zq_ndkdemo_NDKTools */

#ifndef _Included_zq_ndkdemo_NDKTools
#define _Included_zq_ndkdemo_NDKTools
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     zq_ndkdemo_NDKTools
 * Method:    getNDKcontent
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_zq_ndkdemo_NDKTools_getNDKcontent
  (JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

#include "ndkdemoHFile.h" 

JNIEXPORT jstring JNICALL Java_zq_ndkdemo_NDKTools_getNDKcontent
  (JNIEnv *env, jobject obj){
     return (*env)->NewStringUTF(env,"Hellow World，这是NDK的第一行代码");
  }

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := ndkdemomk-jni

LOCAL_SRC_FILES := ndkdemoCFile.c

include $(BUILD_SHARED_LIBRARY)

public class MainActivity extends AppCompatActivity {
    private TextView mDemoText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mDemoText = findViewById(R.id.demo_text);
        String content = NDKTools.getNDKcontent();
        mDemoText.setText(content);
    }
}