Counting standard deviation from parsed XML file
Be careful with instation of same object multiple times for same use- as it may change in use. If and when the first instantiation will be disposed, however, depends. The Java runtime environment traces references, so as long as there are any references to an object in use, the object won't be disposed. Note that the dispose itself does not happen immediately, but sometimes later, the next time when the garbage collector is run. But that is independent from the semantics of the code discussed, thats only a question of memory and performance.
I would use a HashMap for the Data Structure to count deviation. 
Such as this example: 

  HashMap hm = new HashMap();
  // Put elements to the map
  hm.put("Zara", new Double(3434.34));
  hm.put("Mahnaz", new Double(123.22));
  hm.put("Ayan", new Double(1378.00));
  hm.put("Daisy", new Double(99.22));
  hm.put("Qadir", new Double(-19.08));