title: Android String.Format leading zeros issue
body: <p>My string is "1" and i had to add leading zero. I'm using</p>
  
  <pre><code>if (mystring.length() == 1) { 
       mystring = String.format("%02d", mystring);
  }
  </code></pre>
  
  <p>But I get: </p>
  
  <blockquote>
    <p>java.util.IllegalFormatConversionException: %d can't format
    java.lang.String arguments</p>
  </blockquote>
  
  <p>I also already tried with "%02f". Any idea why I'm getting this error ?</p>