Johan,
The question is phrased in such an ambiguous way that it's not even clear if
you're using Java!
If your col1 and set1 refer to the same object then your "foreach" is not
going to get very far (concurrent modification) so I'll assume that col1
!= set1 .
>From a non-functional perspective (acceptable performance, for instance), a
smart implementation of removeAll may loop around the smaller of the two
collections, unlike your "foreach". Now that may seem irrelevant, but if
col1 is a hashed (and well hashed) the removeAll may finish in an acceptable
timeframe if it is an optimised implementation whereas your for loop code
could go on for longer (potentially, unacceptably long).
Functionally, the first problem you face is that both remove and removeAll
are "optional", so either one, or even both of your snippets may just throw
an exception at you. If they both throw the same exception, I suppose you
may even argue that your 2 snippets are functionally the same for those
implementations of the two collections! If only one throws an
UnsupportedOperationException then they are not equivalent.
The question of the Set being sorted or not is also interesting, but may be
a red herring if remove and removeAll are implemented consistently (but they
may not be). If the elements of your collections are Comparables, then "it
is recommended but not strictly required" that (x.compareTo(y)==0) ==
(x.equals(y)). Comparator's compare method contract is similarly loose.
Put this in your test case:
public void testComparingEquals(){
BigDecimal onePointOh = new BigDecimal("1.0");
BigDecimal onePointOhOh = new BigDecimal("1.00");
assertEquals(0, onePointOh.compareTo(onePointOhOh));
assertFalse(onePointOh.equals(onePointOhOh));
}
... yes, it passes!
That means that you could have elements of the same type in both your
collections and still get a different result from each of your two snippets
depending on the Comparator passed in to a sorted collection referred to by
set1.
I think there may be more stuff that can go wrong here, but let's see where
this thread heads off to!
Regards - Cemal
http://jWeekend.com jWeekend
Johan Compagner wrote:
>
> Is this the same?
>
> Set set1 = xxx
> Collection col1 = xxx;
>
> foreach (col in col1)
> set1.remove(col)
>
> or
>
> set1.removeAll(col1);
>
>
> ???
>
>
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