CODEWITHSUNDEEP
kotlinnullable
Jimmy Alvarez
Jimmy Alvarez

Reputation: 587

.add Method of MutableList<E> throws kotlin.KotlinNullPointerException

Please, just keep in mind that I'm ramping up on functional programming hehe.

I have defined a Mutable list like this: 

 var list: MutableList<E>? = null

So, when I try to use list!!.add(E()) this throws a

kotlin.KotlinNullPointerException.

I understand that this is because I assign null to this list when I define it but a didn't get with a right solution thinking about on functional programming aspects how to solve this. Can you suggest me some code or concepts to achieve this situation.

Upvotes: 1

Views: 1266

Answers (2)

Kashif Ahmad
Kashif Ahmad

Reputation: 263

Here is the proper declaration List.

private var mList = mutableListOf<String>()//You can change the String class to your data model

You can add values like this:

mList.add(String)//you can assign your data model class

Upvotes: 0

Ilya
Ilya

Reputation: 23115

You need to initialize the variable with an instance of MutableList before calling any methods on it.

list = mutableListOf<E>() // creates an empty mutable list
list!!.add(E())

If you initialize variable right at the declaration, you even don't need to declare it as nullable and var.

val list = mutableListOf<E>()
...
list.add(E())

Upvotes: 2

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