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

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

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


</manifest>

File fileName = null;
            String sdState = Environment.getExternalStorageState();
            if (sdState.equals(Environment.MEDIA_MOUNTED)) {
                File sdDir = Environment.getExternalStorageDirectory();
                fileName = new File(sdDir, "cache/primer.txt");
            } else {
                //fileName = Context.getCacheDir();
            }
            if (!fileName.exists())
                fileName.mkdirs();
            try {
                FileWriter f = new FileWriter(fileName);
                f.write("hello world");
                f.flush();
                f.close();
            } catch (Exception e) {
                doLog("ERROR:" + e.toString());
            }