In this tutorial, I will show how can I save String Android Internal Storage .txt file Nested Class: 1.File file 2.FileOutputStream fileOutputStream 3.OutputStreamWriter outputStreamWriter Step 1: Android Manifest.xml Permission Add <? xml version ="1.0" encoding ="utf-8" ?> <manifest xmlns: android ="http://schemas.android.com/apk/res/android" package ="com.ruhul.string_save_txt_format" > <uses-permission android :name ="android.permission.WRITE_EXTERNAL_STORAGE" ></uses-permission> <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/Theme.String_save_txt_format" > <activity android :name =".MainActivity" ...