CODEWITHSUNDEEP
javaguava
matiasg
matiasg

Reputation: 2019

Why max and min in Guava for empty arrays throw IllegalArgumentException?

I'm reading the code of Guava's Ints.max(int... array) (and similarly, Ints.min, Longs.min, etc.) They throw an IllegalArgumentException if array.length == 0 (This is Guava 15.0).

I wonder why they do not return the "identity element" in this case, instead of throwing an exception. By "identity element" I mean the element behaving like 1 for product, or 0 for sum. That is, I would expect Ints.min() to be Integer.MAX_VALUE, Ints.max() to be Integer.MIN_VALUE, and so on.

The rationale behind this is that if you split an array in two, the min of the whole array must be the min between the mins of both sub arrays. Or, for the mathematically inclined, the sum over an empty set of real numbers is 0, the product is 1, the union of an empty collection of sets is the empty set, and so on.

Since Guava libraries tend to be carefully produced, I guess there must be an explanation for throwing an exception here. So the question is: why?

Edit: I understand that most people expect max and min of an array to be an element of the array, but this is because max/min of two elements is always one of them. On the other hand, if one regards max/min just as (commutative) binary operations, returning the identity element makes more sense. To me.

Upvotes: 3

Views: 743

Answers (3)

JB Nizet
JB Nizet

Reputation: 692073

Because, IMHO, in 99.99% of the cases, when you ask the minimum element of an array, you want to get an element of this array, and not some arbitrary large value. And thus, most of the time, an empty array is a special condition, that needs a specific treatment. And not handling this special condition is thus a bug, signalled by an exception.

Upvotes: 8

rgettman
rgettman

Reputation: 178303

The minimum/maximum of array values must come from that array. If the array is empty, there there is no value to take. Returning Integer.MAX_VALUE OR Integer.MIN_VALUE here would be wrong, because those values aren't in the array. Nothing is in the array. Mathematically, the answer is the empty set, but that isn't a valid value among possible int values. There is no possible int correct answer, so the only possible correct course of action is to throw an Exception.

Upvotes: 2

djechlin
djechlin

Reputation: 60808

You said it yourself -

The rationale behind this is that if you split an array in two, the min of the whole array must be the min between the mins of both sub arrays. Or, for the mathematically inclined, the sum over an empty set of real numbers is 0, the product is 1, the union of an empty collection of sets is the empty set, and so on.

So [-1] = [-1] union [] but max([-1]) != max([-1] union []). I agree that for product or sum it makes more sense to return the respective identity, but not max/min.

I also prefer the property that max/min(S) be an element of S. Not some element having no relevance with respect to less than and greater than.

In particular if I'm working in a domain with a lot of negative numbers - say temperatures in Northern Canada - a day where my sample of temperatures is empty because the thermometer broke - it should not randomly show up as a relatively very warm day.

Upvotes: 3

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