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

ArrayList maintains its capacity (the size of the internal array) separately from its size (the number of elements added), and the 'set' method depends on the index already having been assigned to an element. There isn't a way to set the size. If you need this, you can add dummy elements with a loop:

for (int i = 200; --i >= 0;) a.add(null);