How to add an "Item" object to an Object ArrayList in kotlin

Question

I have the following class

class Item {
    var name: String = ""

    constructor(n: String) {
        name = n
    }

}

On my main activity I have declared this:

var list: ArrayList<Object> = ArrayList<Object>()

When I try to do this

list.add(Item("Hey friend"))

The compiler complains about type mismatch (Object -> Item) which is obviously true but since Item is also an Object, shouldn't this be fine? I'm pretty sure you can do this in Java, whats the alternative?

I need the list to be of type object because I have to store different stuff in there, so changing it is not an option.

s1m0nw1 · Accepted Answer · 2020-11-24 10:35:57Z

1

The supertype of all types in Kotlin is Any, not Object.

Other things you can improve in var list: ArrayList<Object> = ArrayList<Object>():

make it a val because immutability is preferred
If you need an explicit type declaration, use the interface List<Any
use Kotlin's collection builders listOf()

val items: List<Any> = listOf()`

Also, the class definition can be reduced to

class Item(val name: String) //could even be a data class

edited Nov 24, 2020 at 10:35

answered Nov 24, 2020 at 10:29

s1m0nw1

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2 Comments

Luis Fernandez Over a year ago

One question regarding this, Any is not equivalent to Object right? So if I have a java class with a method that receives a list of type Object, would it work if I feed it a list of type Any?

s1m0nw1 Over a year ago

It is being mapped to Object so yes, you should replace Java Object with Any (read here kotlinlang.org/docs/reference/java-interop.html#mapped-types)

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