Как значения присваиваются при реализации стека?

Меньше - больше,

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tvText = (TextView) findViewById(R.id.tvText);

        try {
            // Create File and Content
            String FILE_NAME = "hallo.txt";
            String content = "Hallo Welt!";

            FileOutputStream fos = openFileOutput(FILE_NAME, MODE_PRIVATE);
            fos.write(content.getBytes());
            fos.close();

            // Read File and Content
            FileInputStream fin = openFileInput(FILE_NAME);
            int size;
            String neuText = null;

            // read inside if it is not null (-1 means empty)
            while ((size = fin.read()) != -1) {
                // add & append content
                neuText += Character.toString((char) size);
            }
            // Set text to TextView
            tvText.setText(neuText);

        } catch (Exception error) {
            // Exception
        }
    }
}