Kotlin : Interface Queue does not have constructors

Question

I'm trying to instantiate an object of Queue using below code

var queue: Queue<Int> = Queue()

But I get this

Interface Queue does not have constructors

No idea what's going on, while searching I found this link.

But I don't understand anything. Please help.

score 35 · Accepted Answer · answered Jun 06 '17 at 12:44

35

Queue is an interface. So you can't instantiate an interface, you have to implement it or instantiate a class that implement it.

For example, you can do var queue: Queue<Int> = ArrayDeque<Int>(). ArrayDeque implements Queue.

answered Jun 06 '17 at 12:44

Kevin Robatel

This will be then a deque not queue I guess? – stephanmg Feb 18 '20 at 23:03
`Deque` extends `Queue` – abitcode Mar 20 '20 at 23:15
Hmm, after going through multiple stackoverflow questions, what I figured out is there are various implementations of the Queue interface. Now my problem is which one should I use. I just want a really basic queue. Should I go with ArrayDeque or LinkedList? – capt.swag Dec 26 '20 at 14:18
`ArrayDeque` is the choice to go for in doubt, because LinkedLists carry significant overhead that is only justified in rare cases: https://stackoverflow.com/questions/6163166/why-is-arraydeque-better-than-linkedlist/6163204#6163204 – xeruf Aug 30 '23 at 09:09

score 13 · Answer 2 · answered Jun 06 '17 at 12:48

13

You trying to create instance of interface but don`t override methods for it. You should use something like this:

val queueA = LinkedList<Int>()
val queueB = PriorityQueue<Int>()

Also you can read more about queue implementations here

answered Jun 06 '17 at 12:48

Silvestr

score 3 · Answer 3 · answered Apr 03 '21 at 04:21

3

Queue is an interface. So you can't instantiate an interface. You should use something like this:

val queue: Queue<Int> = LinkedList()

answered Apr 03 '21 at 04:21

Pavan Bilagi

3 Answers3