import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import static android.os.Environment.getRootDirectory;

public class MainActivity extends AppCompatActivity {
private Button Btn_new;
private TextView TV;
private String UpText,DownText;

Process process = null;
DataOutputStream os = null;
DataInputStream is = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FindViewById();
SetClick();
SetText();
}
private void FindViewById(){
Btn_new=(Button)findViewById(R.id.Btn_new);
TV=(TextView)findViewById(R.id.TV);
}
private void SetClick(){
Btn_new.setOnClickListener(Click);
}
protected Button.OnClickListener Click=new Button.OnClickListener() {
@Override
public void onClick(View v) {
String Edit="11,12,13,14,";
String Edit2=getRootDirectory().toString()+"/etc";
try{
File muFile=new File(Edit2,"libnfc-nxp.conf");
FileOutputStream outStream=new FileOutputStream(muFile,true);
outStream.write((UpText+Edit+DownText).getBytes());
outStream.close();
setTitle("Success");
}catch(IOException e){
setTitle("Error");
TV.setText(e.toString());
}
}
};
private void SetText(){
UpText=""
DownText=""
}
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hjh.texttest3">

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_SETTINGS"/>
<uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<uses-permission android:name="android.permission.INTERNET"/>

</manifest>