CODEWITHSUNDEEP
kotlin
Jules Sam. Randolph
Jules Sam. Randolph

Reputation: 4230

Is there an instanciable MutableList in Kotlin, avoiding java api?

MutableList is an interface, but I cannot find a class in kotlin package that implements it explicitly. Is there any? Furthermore, I would have expected to be a package-scope defined mutableListOf(varargs) symetrically to listOf(varargs). Up until now, I have to use java Collections.

Upvotes: 20

Views: 5513

Answers (3)

mightyWOZ
mightyWOZ

Reputation: 8335

No, as far as Collections are concerned you can not avoid java API's, Because every kotlin collection uses corresponding java collection in one way or another.

Kotlin collection interfaces are just mock interfaces, they don't really exist at runtime. So even if you had a class implementing some kotlin collection interface(ex. MutableList) at runtime it would use corresponding java interface.

for example let's write two kotlin classes implementing kotlin's List and MutableList interfaces respectively

abstract class KotlinList : List<Int>

abstract class KotlinMutableList : MutableList<Int>

when you decompile these classes their signature's change as following (heads up, byte code ahead)

public abstract class com/example/kotlin/KotlinList implements java/util/List kotlin/jvm/internal/markers/KMappedMarker

public abstract class com/example/kotlin/KotlinMutableList implements java/util/List kotlin/jvm/internal/markers/KMutableList

Now both the classes implement java.util.List interface and they also implement kotlin.jvm.internal.markers.KMappedMarker and kotlin.jvm.internal.markers.KMutableList interfaces respectively, so as you can see kotlin interfaces has disappeared and we are left with same old java List and your methods calls will now be addresses as java.util.List.someMethod and not with some kotlin interface. KMutableList and KMappedMarker as their name suggests are marker interfaces used by the the compiler.

In case of KotlinList class if you look inside you will see all mutater methods of java.util.List are generated for you and look similar to the one below

   public boolean add(int var1) {
      throw new UnsupportedOperationException("Operation is not supported for read-only collection");
   }

So as you can see there is no way of avoiding java API's, because they are the foundation of kotlin's collections.

Upvotes: 0

bashor
bashor

Reputation: 8453

Try to use mutableListOf or arrayListOf.

Upvotes: 27

naixx
naixx

Reputation: 1174

You are right, java collections are the only way to get MutableList

Upvotes: 0

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