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);
}

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
}
}*/