Collection array

There are four of tye array type in Kotlin.

• List
• ArrayList
• Array
• IntArray (In the case of Int)

Kotlin List

>>> val a:List<Int> = listOf(1,2,3)
>>> a.add(1)
error: unresolved reference: add

>>> a.javaClass
class java.util.Arrays$ArrayList

Kotlin ArrayList

// kotlin
>>> val a:ArrayList<Int> = arrayListOf(1,2,3)
error: unresolved reference: ArrayList
val a:ArrayList<Int> = arrayListOf(1,2,3)

>>> val a = arrayListOf(1,2,3)
>>> a.add(1)
true
>>> a.javaClass
class java.util.ArrayList

Not work. Because ArrayList is java.util.ArrayList

Kotlin Array

>>> val a:Array<Int> = arrayOf(1,2,3)
>>> a.add(1)
error: unresolved reference: add

>>> a.javaClass
class [Ljava.lang.Integer;

Kotlin IntArray

>>> val a:IntArray = intArrayOf(1,2,3)
>>> a.add(2)
error: unresolved reference: add
a.add(2)

>>> a.javaClass
class [I