title: write and read strings to/from internal file
body: <p>I see a lot of examples how to write String objects like that:</p>
  
  <pre><code>String FILENAME = "hello_file";
  String string = "hello world!";
  
  FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
  fos.write(string.getBytes());
  fos.close();
  </code></pre>
  
  <p>but not how to read them back from internal application file. Most of examples assume specific string length to calculate byte buffer but I do not know what the length will be. Is there an easy way to do so? My app will write up to 50-100 strings to the file</p>