android112 jni 把java的字符串转换成c的字符串，数组处理

package com.itheima.charencode;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends Activity {

    private EditText et;
    static{
        System.loadLibrary("hello");//导入类库
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et = (EditText) findViewById(R.id.et);
        
    }


    public void click1(View v){
        String text = et.getText().toString();
        et.setText(encode(text, text.length()));
    }
    public void click2(View v){
        String text = et.getText().toString();
        et.setText(decode(text, text.length()));
    }
    
    public native String encode(String text, int length);
    public native String decode(String text, int length);
}

#include <jni.h>
#include <string.h>
//把java的字符串转换成c的字符串
char*   Jstring2CStr(JNIEnv*   env,   jstring   jstr)
{
     char*   rtn   =   NULL;
     jclass   clsstring   =   (*env)->FindClass(env,"java/lang/String");
     jstring   strencode   =   (*env)->NewStringUTF(env,"GB2312");
     jmethodID   mid   =   (*env)->GetMethodID(env,clsstring,   "getBytes",   "(Ljava/lang/String;)[B");
     jbyteArray   barr=   (jbyteArray)(*env)->CallObjectMethod(env,jstr,mid,strencode); // String .getByte("GB2312");
     jsize   alen   =   (*env)->GetArrayLength(env,barr);
     jbyte*   ba   =   (*env)->GetByteArrayElements(env,barr,JNI_FALSE);
     if(alen   >   0)
     {
      rtn   =   (char*)malloc(alen+1);         //"\0"
      memcpy(rtn,ba,alen);
      rtn[alen]=0;
     }
     (*env)->ReleaseByteArrayElements(env,barr,ba,0);  //
     return rtn;
}


JNIEXPORT jstring JNICALL Java_com_itheima_charencode_MainActivity_encode
  (JNIEnv * env, jobject obj, jstring jstr, jint lenght){
    char* cstr = Jstring2CStr(env, jstr);
    int i;
    for(i = 0;i < lenght; i++){
        *(cstr + i) += 1;
    }
    return (*env)->NewStringUTF(env, cstr);
}

/*
 * Class:     com_itheima_charencode_MainActivity
 * Method:    decode
 * Signature: (Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_itheima_charencode_MainActivity_decode
(JNIEnv * env, jobject obj, jstring jstr, jint lenght){
    char* cstr = Jstring2CStr(env, jstr);
        int i;
        for(i = 0;i < lenght; i++){
            *(cstr + i) -= 1;
        }
        return (*env)->NewStringUTF(env, cstr);
}

 数组处理：

package com.itheima.array;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;

public class MainActivity extends Activity {

    static{
        System.loadLibrary("hello");
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    int[] arr = {1,2,3,4,5};

    public void click(View v){
        arrayEncode(arr);
        for (int i : arr) {//上面已经对数组内存进行了改变，所以此处是修改后的数组
            System.out.println(i);
        }
    }
    
    public native void arrayEncode(int[] arr);
}
/*
hello.c文件：

#include <jni.h>

JNIEXPORT void JNICALL Java_com_itheima_array_MainActivity_arrayEncode
  (JNIEnv * env, jobject obj, jintArray jintarr){//jintArray是整型数组，jni中所有的数组都是指针类型
    //拿到整型数组的长度以及第0个元素的地址
     //jsize  (*GetArrayLength)(JNIEnv*, jarray);jsize就是int类型（jni.h文件都有定义）
    int length = (*env)->GetArrayLength(env, jintarr);
     //jint*  (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);jint就是int类型
    int* arrp = (*env)->GetIntArrayElements(env, jintarr, 0);//得到第0个元素的地址

    int i;
    for(i = 0;i < length; i++){//数组是连续的内存空间，有了数组长度和数组第0个元素地址就相当于拿到了所有数组。
        *(arrp + i) += 10;//每个元素加10
    }
}*/