Kotlin Basic Input/Output
In this article, you will learn to display output to the screen, and take input from the user in Kotlin.
Koltin Output
You can use println()
and print()
functions to send output to the standard output (screen). Let’s take an example:
fun main(args : Array<String>) {
println("Kotlin is interesting.")
}
When you run the program, the output will be:
Kotlin is interesting.
Here, println()
outputs the string (inside quotes).
Difference Between println() and print()
print()
– prints string inside the quotes.println()
– prints string inside the quotes similar likeprint()
function. Then the cursor moves to the beginning of the next line.
When you use println()
function, it calls System.out.println()
function internally. (System.out.println()
is used to print output to the screen in Java).
If you are using IntelliJ IDEA, put your mouse cursor next to println
and go to Navigate
> Declaration
( Shortcut: Ctrl + B . For Mac: Cmd + B), this will open Console.kt
(declaration file). You can see that println()
function is internally calling System.out.println()
.
Similarly, when you use print()
function, it calls System.out.print()
function.
Example 1: print() and println()
fun main(args : Array<String>) {
println("1. println ");
println("2. println ");
print("1. print ");
print("2. print");
}
When you run the program, the output will be:
1. println 2. println 1. print 2. print
Example 2: Print Variables and Literals
fun main(args : Array<String>) {
val score = 12.3
println("score")
println("$score")
println("score = $score")
println("${score + score}")
println(12.3)
}
When you run the program, the output will be:
score 12.3 score = 12.3 24.6 12.3
Kotlin Input
In this section, you will learn to take input from the user..
To read a line of string in Kotlin, you can use readline()
function.
Example 3: Print String Entered By the User
fun main(args: Array<String>) {
print("Enter text: ")
val stringInput = readLine()!!
println("You entered: $stringInput")
}
When you run the program, the output will be:
Enter text: Hmm, interesting! You entered: Hmm, interesting!
It’s possible to take input as a string using readLine()
function, and convert it to values of other data type (like Int
) explicitly.
If you want input of other data types, you can use Scanner
object.
For that, you need to import Scanner
class from Java standard library using:
import java.util.Scanner
Then, you need to create Scanner
object from this class.
val reader = Scanner(System.`in`)
Now, the reader object is used to take input from the user.
Example 4: Getting Integer Input from the User
import java.util.Scanner
fun main(args: Array<String>) {
// Creates an instance which takes input from standard input (keyboard)
val reader = Scanner(System.`in`)
print("Enter a number: ")
// nextInt() reads the next integer from the keyboard
var integer:Int = reader.nextInt()
println("You entered: $integer")
}
When you run the program, the output will be:
Enter a number: -12 You entered: -12
Here, reader
object of Scanner
class is created. Then, the nextInt()
method is called which takes integer input from the user which is stored in variable integer.
To get Long
, Float
, double
and Boolean
input from the user, you can use nextLong()
, nextFloat()
, nextDouble()
and nextBoolean()
methods respectively.
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