How to add an item to an ArrayList in Kotlin

Question

User · Answer

If you want to specifically use java ArrayList then you can do something like this:

fun initList(){
    val list: ArrayList<String> = ArrayList()
    list.add("text")
    println(list)
}

Otherwise @guenhter answer is the one you are looking for.

User · Answer

If you have a MUTABLE collection   val list   mutableListOf 1  2  3  list    4   If you have an IMMUTABLE collection   var list   listOf 1  2  3  list    4   note that I use val for the mutable list to emphasize that the object is always the same  but its content changes   In case of the immutable list  you have to make it var  A new object is created by the    operator with the additional value

User · Answer

For people just migrating from java  In Kotlin List is by default immutable and mutable version of Lists is called MutableList   Hence if you have something like    val list  List lt String gt    ArrayList     In this case you will not get an add   method as list is immutable  Hence you will have to declare a MutableList as shown below    val list  MutableList lt String gt    ArrayList     Now you will see an add   method and you can add elements to any list

User · Answer

You can add element to arrayList using add   method in Kotlin  For example  arrayList add 10   Above code will add element 10 to arrayList  However  if you are using Array or List  then you can not add element  This is because Array and List are Immutable  If you want to add element  you will have to use MutableList  Several workarounds   Using System arraycopy   method  You can achieve same target by creating new array and copying all the data from existing array into new one along with new values  This way you will have new array with all desired values Existing and New values  Using MutableList   Convert array into mutableList using toMutableList   method  Then  add element into it  Using Array copyof    Somewhat similar as System arraycopy   method

[kotlin] How to add an item to an ArrayList in Kotlin?

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