title: Why Array list increase dynamically and not decrease dynamically
body: <p>I have a simple doubt , Arraylist increase its size with factor ( 2,1.5 or old_capacity*3/2 +1 or what ever) as it got full , and add new element in it. Then why dont it decrease it size dynamically if number is removed by some factor. Like if I have 10000 element in arraylist and  at particular time all the elements are  removed , only 100 elements are their in array list now It still hold 10000 object memory. Why i have to call trimTosize() or something? why it is not their automatically? Did I miss something .. ? Please dont tell me how to do it, I want to know why we have to do it ?? 
  Thanks </p>