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Kotlin Keywords and Identifiers

Every programming language has certain predefined words which carries some special meaning. They are known as keywords. Keywords cannot be used as an identifier.

An identifier is the name given to a variable, class, function, interface etc.

For example, name is an identifier here:

val name: String = "emp_name"

However, in Kotlin we can use some of the keywords as an identifier depending upon their type.

Types of keywords

There are two types of keywords in Kotlin:

  1. Hard keyword

  2. Soft keyword

Hard Keywords

Hard keywords cannot be used as an identifier. An error will be thrown if they are used as an identifier.

For example, in the HelloWorld program we created a function using the fun keyword. If we try creating a variable with name fun, we'll get an error.

val fun = 5   // Error

The Hard keywords in Kotlin are:

Hard keywords

as

break

class

continue

do

else

false

for

fun

if

in

interface

is

null

object

package

return

super

this

throw

true

try

typealias

typeof

val

var

when

while

Soft Keywords

Soft keywords are treated as keywords in a certain context, whenever they are applicable. In other contexts, they can be used as an identifier. For example, private is considered as keyword when we are setting the visibility of a class or a member. In another context, it can be used as an identifier.

val private = 5 // No Error

The soft keywords in Kotlin are:

by

which

constructor

delegate

dynamic

field

file

finally

get

import

init

param

property

receiver

set

setparam

where

actual

abstract

annotation

companion

const

crossinline

data

enum

expect

external

final

infix

inline

inner

internal

lateinit

noinline

open

operator

out

override

private

protected

public

reified

sealed

suspend

tailrec

vararg

Summary

In this tutorial, we studied about keywords and identifiers. We will use and study most of the keywords in this tutorial series.

Next, we will study about variables in Kotlin.