Try the following example:
if (!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
//handle case of no SDCARD present
} else {
String dir = Environment.getExternalStorageDirectory()+File.separator+"myDirectory";
//create folder
File folder = new File(dir); //folder name
folder.mkdirs();
//create file
File file = new File(dir, "filename.extension");
}
Don't forget to add the permission to your AndroidManifest:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
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