What does comment.charAt(i % comment.length()) do?

Question

I don't understand the % comment.length bit of the following code:

comment.charAt(i % comment.length())

Does the part between the brackets convert to an integer with the value that represents i in relation to the comment length?

For instance, if:

comment = "test"
i = 2

what would comment.charAt(i % comment.length()) be?

2%4 => 2. And character at index 2 is **s**. Am I missing anything ? — Mahesh, Jan 25 '12 at 13:54
Well, you're basically saying `comment.charAt(0.5)`, which doesn't work as the `charAt()` method takes only positive integers as its argument. — fireshadow52, Jan 25 '12 at 13:55
@fireshadow52 - Might want to [re-calculate that](https://www.google.com/search?q=2+%25+4). — Rob Hruska, Jan 25 '12 at 13:57
%fireshadow52: no % is not the division operator is the modulo operator and works on integers — Matteo, Jan 25 '12 at 13:57
@RobHruska Right... I forgot the modulo operator only returned integers. Well in that case, the result would be "s". — fireshadow52, Jan 25 '12 at 13:59
http://stackoverflow.com/questions/90238/whats-the-syntax-for-mod-in-java is relevant. — Mike Samuel, Jan 25 '12 at 14:06

Thomas · Answer 1 · 2012-01-25T14:40:13.210

6

% is the modulo operator, thus for your example i % comment.length() would resolve to 2 % 4 = 2. This would return the third character (at index 2).

The modulo operation seems to be a safeguard for cases where i >= comment.length().

Consider the following case: i = 11 and comment = "test". If you just use comment.chatAt(i) you'd get an exception since there are only 4 characters. The modulo operation would wrap that around and result in 11 % 4 = 3 and return the fourth character (index 3) in that case.

edited Jan 25 '12 at 14:40

answered Jan 25 '12 at 13:54

Thomas

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Thanks! I understand! It returns the remainder of the division ! so 13 % 3 = 1, 5 % 3 = 2, 5 % 2 = 1 and so on. – Kees Koenen Jan 25 '12 at 19:28
Exactly! If you like this answer... you should choose it! – ByteMe May 11 '12 at 02:07

score 2 · Answer 2 · answered Jan 25 '12 at 13:57

% is the modulo operator: it gives you the remainder of an integer division

10 % 3 = 1

as 10 / 3 = 3 with a remainder of 1

Your statement just ensures that the function argument will be less then the string length.

But I would rather check this in another way. It is pretty counterintuitive to ask for character at position 11 in a string long 10 characters and get the character at position 1 instead of a warning or error message.

What does comment.charAt(i % comment.length()) do?

2 Answers2