I want to make this class immutable. How to optimize performance?

Question

Hi,
I designed an immutable class for other people to use. And I'm wondering if there's any way to optimize it for performance.
ie.
class MyImmutableList
  final List myList;
  public MyImmutableList(List list)
    myList = list;
  public MyImmutableList append(Item item)
    List copy = myList.copy();
    copy.append(item);
    return new MyImmutableList(copy);
}But I find that many times, other people use the class like this:
someList = someList.append(item);So in a case like this, append() is unnecessarily making a copy of the list.
Is there anyway to optimize this?
Thanks
-Cuppo
Edited by: CuppoJava on 20-Jul-2008 5:44 AM
Edited by: CuppoJava on 20-Jul-2008 5:44 AM

Answer 1

DrClap wrote:
Well, of course, what else should they do when the method returns an ImmutableList?
What I would do with that append() method would be to remove it from the API entirely. The class is supposed to be immutable? Then it doesn't need an append() method. Unless, of course, the append() method isn't meant to change the state of the object, which seems a bit, let's say, unintuitive. Returning a copy of the list with the object appended then wouldn't change the state of the object, but it would return a new object. Which in fact is what the code does. But why? I'm like those other people, I would do that too. I don't understand the purpose of the method.The Defence calls java.math.BigDecimal
>
BigDecimal, would it be fair to say, you are an immutable class?
It would.
Would it also be true to say that you have an add() method?
I do
And would it be fair to say that adding could be construed as a mutating operation?
I suppose so
And what does this method do, given that you claim to be immutable?
It returns a new object which is the result of the add() operation
Thankyou