java arraylist ensureCapacity not working

Question

Either I\'m doing this wrong or i\'m not understanding how this method works.

ArrayList a = new ArrayList();
a.ensureCapacity(200         


        

Answer 1

Ensuring capacity isn't adding items to the list. You can only get element 190 or add at element 190 if you've added 191 elements already. "Capacity" is just the number of objects the ArrayList can hold before it needs to resize its internal data structure (an array). If ArrayList had a getCapacity(), then doing this:

ArrayList a = new ArrayList();
a.ensureCapacity(200);
System.out.println(a.size());
System.out.println(a.getCapacity());

would print out 0 and some number greater than or equal to 200, respectively