Kotlin - How to correctly concatenate a String

Question

A very basic question  what is the right way to concatenate a String in Kotlin   In Java you would use the concat   method  e g   String a    Hello    String b   a concat  World       b   Hello World   The concat   function isn t available for Kotlin though  Should I use the   sign

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Similar to  Rhusfer answer I wrote this  In case you have a group of EditTexts and want to concatenate their values  you can write  listOf edit 1  edit 2  edit 3  edit 4  joinToString separator    quot  quot     it text toString      If you want to concatenate Map  use this  map entries joinToString separator    quot    quot    To concatenate Bundle  use bundle keySet   joinToString  quot    quot     key - gt   quot  key   bundle key   quot     It sorts keys in alphabetical order  Example  val map  MutableMap lt String  Any gt    mutableMapOf  quot price quot  to 20 5  map     quot arrange quot  to 0 map     quot title quot  to  quot Night cream quot  println map entries joinToString separator    quot    quot        price 20 5  arrange 0  title Night cream  val bundle   bundleOf  quot price quot  to 20 5  bundle putAll bundleOf  quot arrange quot  to 0   bundle putAll bundleOf  quot title quot  to  quot Night cream quot    val bundleString       bundle keySet   joinToString  quot    quot     key - gt   quot  key   bundle key   quot    println bundleString      arrange 0  price 20 5  title Night cream

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yourString     newString   This way you can concatenate a string

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I agree with the accepted answer above but it is only good for known string values  For dynamic string values here is my suggestion     A list may come from an API JSON like       quot names quot            quot Person 1 quot          quot Person 2 quot          quot Person 3 quot                       quot Person N quot         var listOfNames   mutableListOf lt String gt      val stringOfNames   listOfNames joinToString  quot    quot        quot    quot   lt - a separator for the strings  could be any string that you want     Posible result    Person 1  Person 2  Person 3       Person N  This is useful for concatenating list of strings with separator

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There are various way to concatenate strings in kotlin  Example -   a    Hello    b   World     Using   operator a b Using plus   operator  a plus b    Note -   is internally converted to  plus   method only  In above 2 methods  a new string object is created as strings are immutable  if we want to modify the existing string  we can use StringBuilder  StringBuilder str   StringBuilder  Hello   append  World

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kotlin String has a plus method   a plus b    See https   kotlinlang org api latest jvm stdlib kotlin -string plus html for details

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String Templates Interpolation In Kotlin  you can concatenate using String interpolation templates  val a    quot Hello quot  val b    quot World quot  val c    quot  a  b quot   The output will be  Hello World  The compiler uses StringBuilder for String templates which is the most efficient approach in terms of memory because   plus   creates new String objects   Or you can concatenate using the StringBuilder explicitly  val a    quot Hello quot  val b    quot World quot   val sb   StringBuilder   sb append a  append b  val c   sb toString    print c   The output will be  HelloWorld New String Object Or you can concatenate using the     plus   operator  val a    quot Hello quot  val b    quot World quot  val c   a   b      same as calling operator function a plus b   print c   The output will be  HelloWorld  This will create a new String object

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Try this  I think this is a natively way to concatenate strings in Kotlin   val result   buildString      append  a       append  b      println result      you will see  ab  in console

User · Answer

Yes  you can concatenate using a   sign  Kotlin has string templates  so it s better to use them like   var fn    Hello  var ln    World      fn  ln  for concatenation    You can even use String plus   method

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