I have: ```val map: Map<Int, String> = ... ``` If I create a list via: ```val list: List<String> = m...

# getting-started

[statmark56]

I have:

val map: Map<Int, String> = ...

If I create a list via:

val list: List<String> = map.values.toList()

Will I cause memory allocation: 2*N, where N = size of String entries (1 from map, 1 from the list)?

[Jacob]

I’m guessing:
The actual strings will only be in memory once
There will already be N references to the strings before you call values.toList()
There will be at least 2N References when the call completes.
There will be up to 3N references during the calls but the intermediate list will eventually get garbage collected

So short answer. Yes, 2N but 2N references, not 2n Strings

Disclaimer. I’m just making a mildly educated guess

[Johann Pardanaud]

use asList to use the original array

[Klitos Kyriacou]

That could be nice, but map.values is a collection. There's no technical reason asList couldn't exist for a collection, but it doesn't. It's only defined for arrays.

[Johann Pardanaud]

oh you're right, sorry for the misleading answer!

[Johann Pardanaud]

what about asIterable?

[Klitos Kyriacou]

map.values is a Collection, which is already an Iterable.

The main point for the OP is don't call toList() unless you absolutely need a List.

[Johann Pardanaud]

right, I really didn't help there, sorry 😅

[statmark56]

Thanks guys.
Completely agree with @Jacob for 2N -> references, not actual object allocation.

Now, will the number of references ever cause OutOfMemoryException in jvm?

[Wout Werkman]

This depends on the implementation of Map. Map.values will most likely be implemented as a view. So it will most likely have allocations independent of N.
.toList() will always introduce at least N, and most likely not more

[Jacob]

Yeah I’m changing my answer No allocations until toList is called which will allocate N references. not 2N

[ephemient]

allocates a list object with a backing array of size N for. not sure what you mean by "allocate N references", that's kind of odd phrasing since references aren't what's being allocated

[ilya.gorbunov]

That could be nice, but map.values is a collection. There's no technical reason asList couldn't exist for a collection,

@Klitos Kyriacou For example, one reason is that List requires implementing indexed access to elements and reverse iteration and Collection doesn't provide these.

[Klitos Kyriacou]

Good point, Ilya, thanks.