title: Get the last x day from a string in android (e.g. 20140310 , last 2 day , return 20140308)
body: <p>How can serve a string as a date and reduce 2 day, 
  after that return the result as an string ? </p>
  
  <p>Just similar to the title example? Thanks</p>
  
  <p>This is some related code but it seems deduct from current date and not output as a string like e.g. 20140308, thanks</p>
  
  <pre><code>Calendar calendar = Calendar.getInstance(); 
  calendar.add(Calendar.DATE, -2);
  </code></pre>