How to write text in Lock Screen?

Question

I have searched in SO to find a way to write some text in lock Screen like so many apps in Google Play. There are some similar questions about this but unfortunately I haven't find a clear answer which works for me. I have tested this on my Galaxy S5 :

String message = "This is a test";
Settings.System.putString(context.getContentResolver(),
        Settings.System.NEXT_ALARM_FORMATTED, message);

(I have used the right permission for that)

but it doesn't work for me(or maybe I don't know where and how to use it in my code) Is there anyone to give me a clear answer about how to write some text in lock screen?