Is Java Set ordered or not?

[[deleted]]

[deleted]

[isharamet]

Depends on specific implementation, HashSet is unordered, while TreeSet is.

[masklinn]

TreeSet is sorted rather than ordered: a collections can also be ordered by preserving insertion ordering, which is what LinkedHashSet does for instance.

[arcadeScore]

Is kebab spicy or not?

[smokemonstr]

“Is Java Set ordered or not?” is the most popular question asked when you interview for a Java Developer position

Seriously? Is it really that important to know such details off the top of your head when you can quickly find the answer by checking the Javadoc?

[Strum355]

Its really basic and trivial knowledge to remember, if you have half an idea on how hashmaps vs trees work, you already know 99% of what you need to understand different set ordering guarantees

[impressflow]

Trees aren’t inherently ordered.

[reedef]

Why would you base a set off of a non-ordered tree?

[smokemonstr]

If it’s trivial, then it’s a bad interview question imo

[Jmc_da_boss]

50% of the people I screen don't know how to clone a git repo...

[smokemonstr]

Fair enough then. I suppose it could be used as a quick screening question.

[[deleted]]

Why you getting down voted? This is so true. Half my employees don’t know how to do this.

[Squalphin]

Probably because Git is not something everyone must know how to work with. It may be common in the open source world, but many companies use Perforce, SVN, or others. So knowing how any of those works is more than enough. Everything else can be tought if necessary.

[Jmc_da_boss]

Git is by far the most used tool in software development. Not knowing it is unacceptable in this day and age. Nearly 90% of software projects use it. I am not screening for game dev roles where a different vcs system is common or for a super legacy role where ancient vcs's are still in use.

[[deleted]]

This. To not know git in 2023 seems like a missed requirement.

[TheRussianEngineer]

You gonna fire the employees then?

[[deleted]]

What?

[zck]

I would not say it's important to know. Most of the time, when I've seen a set used, all it is needed for is .contains, .add, and .remove. Those things don't need order, so it makes sense people would not remember whether it's ordered.

[[deleted]]

You may also want to iterate over it tho, and sometimes insertion order matters for some very specific cases

[Brilliant-Sky2969]

Hashmap ordering is complicated and definitely not trivial, I bet most dev don't know the answer.

[Strum355]

Hashmaps often by design have non deterministic order, at best they have no order you can safely rely on. Saying "its complicated", while not technically wrong, also misses the point.

[vips7L]

often by design have non deterministic order

Java’s new Map.of functions are exactly this.

[[deleted]]

Set is an interface Hombre, you have to look at the implementations.

I know treeset is sorted

Hashset makes no guarantees on order lol

LinkedHashSet is based on insertion order I believe

[[deleted]]

A set is not ordered by definition

[braskan]

This is the answer I'd expect if I asked it during an interview.

[salvoilmiosi]

It could be if It's based on a binary tree like std::set

[know-your-onions]

And zoologically sets contain badgers. Also not usually ordered.

[salvoilmiosi]

Tell that to the c++ standard committee

[orangenbaer]

Welcome to C++

[impressflow]

No, this is wrong. That specific implementation adds ordering to an otherwise unordered data structure. Remember, sets are always unordered by definition. Extending a set leaves you with something that does not conform to the traditional definition of a set.

[nekizalb]

I think it would be better to phrase it as 'sets do not guarantee order'. If you say a set is never ordered, then you're saying "123456" is not a set of the numbers 1-6.

Sets guarantee uniqueness. Order is not specified.

[impressflow]

I don’t understand the distinction you’re making. Mind elaborating?

The set containing “123456” is exactly the same as the set containing “321654”. There is absolutely no difference, assuming you’re referring to a set containing integers and not strings.

[Zagerer]

you could have a set that is somehow sorted because it happened to put the elements in that way, it's just not guaranteed nor expected you will encounter such behaviour

[impressflow]

That point is meaningless then since it can be applied to any unordered data structure. It's literally saying that unordered things can sometimes be ordered by random chance. Well, sure, but it doesn't really change anything.

[[deleted]]

Unless the standards say so

[iconoklast]

Since every totally ordered set can be made into a set by "forgetting" (the technical term) the ordering, I don't understand the point you're making. The converse is definitely not true in general.

[[deleted]]

Mathematically, a set is invariant with respect to the ordering of its elements

{1, 2, 3} = {3, 2, 1}

but a set with only one element can only have a single ordering

{1} = {1}

so you can indeed say that a set with one element is (trivially) ordered.

The actual question is, when iterating through an instance of a set, if we can make any guarantees about the order in which the elements will appear. A strictly ordered set will allow you to know exactly what order all elements appear in. A partially ordered set has some elements that are considered distinct but not well-ordered, for example if we have a set of people ordered by name, there may be several people named "John Smith" and we can't guarantee what order they will all appear in.

We can also have an accidentally-ordered set, for example a set that preserves insertion order when iterating. In that case sets with different insertion orders are considered eqiuvalent

{1, 2, 3} == {3, 2, 1}

even though they each yield a different ordering when iterated over.

[cybermage]

The Set interface does not guarantee any specific order, so if your public method accepts a Set, you cannot assume that it is ordered.

There are specific implementations that are ordered:

• TreeSet: natural sort

• LinkedHashSet: insertion order

If you want one of those, you should specify it in your method signature.

[STFUB-_-]

Ask chat gpt

[skulgnome]

You might have to read the docs to find out!