How to check if SharedPreferences exists or not

Well, one could do:

    SharedPreferences sharedPrefs = getSharedPreferences("sp_name", MODE_PRIVATE);
    SharedPreferences.Editor ed;
    if(!sharedPrefs.contains("initialized")){
        ed = sharedPrefs.edit();

        //Indicate that the default shared prefs have been set
        ed.putBoolean("initialized", true);

        //Set some default shared pref
        ed.putString("myDefString", "wowsaBowsa");

        ed.commit();
    }  

SharedPreferences has a contains(String key) method, which can be used to check if an entry with the given key exists.

http://developer.android.com/reference/android/content/SharedPreferences.html

Another solution:

If you know the exact number of preferences you have you can:

public void isPreferencesSet(Context context){
    SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
    return (sharedPreferences.getAll().size() == exactNumberOfPreferences);
}

This works because the preferences file stored in /data/data/myApp/shared_prefs/myApp_prefrences.xml contains a preference's value pair only if its value has been set.