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?
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.
kotlin.String
has a plus
method:
a.plus(b)
See https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/plus.html for details.
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 $ln"
for concatenation.
You can even use String.plus()
method.
yourString += "newString"
This way you can concatenate a string
Similar to @Rhusfer answer I wrote this. In case you have a group of EditText
s and want to concatenate their values, you can write:
listOf(edit_1, edit_2, edit_3, edit_4).joinToString(separator = "") { it.text.toString() }
If you want to concatenate Map
, use this:
map.entries.joinToString(separator = ", ")
To concatenate Bundle
, use
bundle.keySet().joinToString(", ") { key -> "$key=${bundle[key]}" }
It sorts keys in alphabetical order.
Example:
val map: MutableMap<String, Any> = mutableMapOf("price" to 20.5)
map += "arrange" to 0
map += "title" to "Night cream"
println(map.entries.joinToString(separator = ", "))
// price=20.5, arrange=0, title=Night cream
val bundle = bundleOf("price" to 20.5)
bundle.putAll(bundleOf("arrange" to 0))
bundle.putAll(bundleOf("title" to "Night cream"))
val bundleString =
bundle.keySet().joinToString(", ") { key -> "$key=${bundle[key]}" }
println(bundleString)
// arrange=0, price=20.5, title=Night cream
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.
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")
Source: Stackoverflow.com