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

So as others have mentioned ensureCapacity isn't for that. It looks like you want to start out with an ArrayList of 200 nulls? Then this would be the simplest way to do it:

ArrayList a = new ArrayList(Arrays.asList( new String[200] ));

Then if you want to replace element 190 with "test" do:

a.set(190, "test");

This is different from

a.add(190, "test");

which will add "test" in index 190 and shift the other 9 elements up, resulting in a list of size 201.

If you know you are always going to have 200 elements it might be better to just use an array.