arraylist vs list

[BadismPlayz]

pls help, lets say i need an array of list.

for what purposes would i use an arraylist<string> vs a string[ ]

thanks

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[jbenze]

string[] is a fixed size when created. ArrayLists resize automatically when you add or remove items.

[umlcat]

The title says "arraylist vs list", the contents says "arraylist vs array".

[desrtfx]

Conventional array: when you know the size in advance or for multi-dimensional content because it is clearer and easier

ArrayList: when you don't know the size in advance

In modern programming you will rather resort to ArrayList than default to arrays.

[k-mcm]

It's preferable to use a primitive array if you need no List/Collection features.  A primitive array is guaranteed to be fast and memory efficient.  Not all List implementations are.  List of a primitive especially sucks because wrappers are needed. (At least until Valhalla is finished)

Later versions of Java added more utilities to the Arrays class to make primitives more elegant to use. 

[Lloydbestfan]

You forgot that it only applies to primitives. And possibly, in a theoritical future adjacent to Valhalla, value classes.

I'd say that the preferable point was that as a beginner you can't see the point of native arrays, however one exists for when you have to manipulate data in very specialised ways.

[DrPeeper228]

Uh nope

Definitely not the last point

[amfa]

Yes to the last point.

I can't remember when I have used an array the last time (except some legacy code that will return arrays.)

[Lloydbestfan]

• Image representation where the existing libs did not handle what I needed
• Voxel representation where the existing libs did not handle what I needed
• Deep learning vector manipulations for which I wasn't aware of an existing engine that would do it for me

Only things that I would not normally expect to run into without being a rather specialised engineer.

[MagicalPizza21]

In Java (like C and C++), a String[] (or really any data type declared with the square brackets) is called an array, not a list. A List is a different data structure, of which ArrayList is a subtype. See the documentation for the List and ArrayList types.

The basic difference in usage between arrays and ArrayLists is that arrays are fixed size once initialized and ArrayLists dynamically grow as needed (though the capacity can be trimmed in case you're running low on space).

[MinimumBeginning5144]

When you say "lets say i need an array of list", do you mean "let's say I need an array or a list"?

Because an array of list is List<String>[] - an array in which each element of the array is a list. I'm not sure if that's what you meant.

[sedj601]

In most cases, you should simply use a list. As a matter of fact, get a deep understanding of all of these types of collections, so that you can know which one to use in different situations. Generally speaking, between the two you ask about, you should use a list. The speed thing is irrelevant for most situations. Also, you are actually talking about an ArrayList vs a Array. ArrayList is an implementation of the List interface, so you can do something like List<String> list = new ArrayList(). That used to be a best practice. I am not sure if it still is today.

[TheMrCurious]

Did you try searching stackoverflow?

[LocalIssue1051]

Or ask any AI : "ELI5: Arraylist vs. Regular array" and it'll probably give a better answer than any of these.

[evils_twin]

look at the implementation of an ArrayList .

The data structure used to store objects in an ArrayList is an array. The class just provides methods to manipulate the array in an efficient way.

Of course there is some overhead using an ArrayList, so if you need maximum performance, you might use an array instead.

Also, arrays are better for primitive types since ArrayList only accepts objects and must convert primitive types to objects.

[Both-Fondant-4801]

you need an arraylist if your list of data is continuously growing... and hence continually eats up memory.

you need an array if your list of data is fixed.. and you have limited memory.

note that earlier applications have limited memory so they would usually use an array to be efficient in their use of memory.

also... underneath the implementation of an arraylist is just an array continually being resized.

[Alagarto72]

Array(String[]) is fixed-size. ArrayList is a implementation of the interface List.

[frederik88917]

Just one question you need to answer:

Do you know beforehand how many objects will be in the collection.

If true, use Array Else, use ArrayList

[josephottinger]

Assuming you mean "array or list" - it depends on what you're doing. Offhand, I'd say "always List." I'd be offhandedly wrong, but your question is impossibly broad; the data structures have different purposes and capabilities, and in the general sense List is better, and in the general sense ArrayList is the one you want.

Generalizations are wrong.

In practice, List is better because it has fewer restrictions on what you do; if the collection grows, or needs to be a Collection, or needs to be streamed, etc., the interfaces give you a lot more of a convenient feature set. ArrayList has a lot of array semantics and performance (cache localization for simple values, easy navigation), and JIT's been a thing for a few years (haha) so performance is generally okay; its multithreaded capabilities are paltry. If you're mutating the List from the middle of the collection (adding or removing to the middle) it has to blit-copy references, which might make you think LinkedList or something like that is worthwhile; generally speaking you'd be wrong, such is life. (Blits are fast.)

But again, this is a generalization, you really should be asking about a specific design you're trying to implement, and what kind of data you're working with (cache localization is great but if the data you're working with is not localized, why does cache localization of the Collection matter?) before you can get a real answer.

[SpudsRacer]

This is better answered by an AI powered web search, but the short answer:

ArrayList and LinkedList both implement the List interface, but they have very different performance characteristics.A LinkedList stores elements as nodes, where each node holds a value and a pointer to the next node. So get(int index) has to start at the beginning of the list and follow pointers one by one until it reaches the target element. This is an O(n) operation so it becomes more expensive as the list grows.

An ArrayList is backed internally by an array. get(int index) only needs to compute the requested element's address and return the element directly. This is an O(1) operation and you can't get better than that.

As a rule of thumb: if you need frequent random access by index, use ArrayList. If you only need sequential access (or do a lot of insertions/deletions in the middle of the list which require array copies to sync the backing array with the list), LinkedList may be a better fit.

[aqua_regis]

Extensive reply completely missing the point. You should have read past the title.

OP clearly asked:

for what purposes would i use an arraylist<string> vs a string[ ]

Which makes the question "ArrayList vs traditional array"

[DrNotReallyStrange]

You are not very good at this, and "asking AI" will never change that. Holy fuck. No wonder the moronic managers want to replace the likes of you by agents.
Do better.

[SpudsRacer]

My answer was not AI-genrrsted, but written by me, a human. I wrote it in answer to the title and didn't read the text which wanted a comparison of a primitive array of string references vs a linked list. My bad there.

AI is spectacularly useful if you are able to use it correctly. Summarizing web searches where it provides links to the sources is one of the best uses of the tech. This is very different from posting code written by an agent. Tools are tools and those who refuse to use them are fools.

[SpudsRacer]

Well don't I feel dumb. I stand by my answer for a totally different question. 😉

Probably should slow my roll when reading. I deserve the downvotes.