Best Loop Idiom for special casing the last element

Question

I run into this case a lot of times when doing simple text processing and print statements where I am looping over a collection and I want to special case the last element (

Answer 1

...

String[] items = { "dog", "cat", "bat" };
String res = "[";

for (String s : items) {
   res += (res.length == 1 ? "" : ", ") + s;
}
res += "]";

or so is quite readable. You can put the conditional in a separate if clause, of course. What it makes idiomatic (I think so, at least) is that it uses a foreach loop and does not use a complicated loop header.

Also, no logic is duplicated (i.e. there is only one place where an item from items is actually appended to the output string - in a real world application this might be a more complicated and lengthy formatting operation, so I wouldn't want to repeat the code).