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         


        

Answer 1

kotlin.String has a plus method:

a.plus(b)

See https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/plus.html for details.

Answer 2

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 = "") { it.text.toString() }

If you want to concatenate HashMap, use this:

map.entries.joinToString(separator = ", ")
// Result:
// id=123, name=John, surname=Smith

Answer 3

In Kotlin, you can concatenate using string interpolation / templates:

val a = "Hello"
val b = "World"
val c = "$a $b"

The output will be: Hello World

Or you can concatenate using the + / plus() operator:

val a = "Hello"
val b = "World"
val c = a + b   // same as calling operator function a.plus(b)

print(c)

The output will be: HelloWorld

Or you can concatenate using the StringBuilder.

val a = "Hello"
val b = "World"

val sb = StringBuilder()
sb.append(a).append(b)
val c = sb.toString()

print(c)

The output will be: HelloWorld

Answer 4

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
{
   "names": [
      "Person 1",
      "Person 2",
      "Person 3",
         ...
      "Person N"
   ]
}
var listOfNames = mutableListOf<String>() 

val stringOfNames = listOfNames.joinToString(", ") 
// ", " <- 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.

Answer 5

There are various way to concatenate strings in kotlin Example -

a = "Hello" , b= "World"

1. Using + operator a+b

2. 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")

Answer 6

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.