How can I get a random number in Kotlin

Question

A generic method that can return a random integer between 2 parameters like ruby does with rand 0  n    Any suggestion

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Examples random in the range  1  10       val random1    0  10  shuffled   last     or utilizing Java Random  val random2   Random   nextInt 10    1

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Below in Kotlin worked well for me   fromNumber rangeTo toNumber   random    Range of the numbers starts with variable fromNumber and ends with variable toNumber  fromNumber and toNumber will also be included in the random numbers generated out of this

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Kotlin standard lib doesn t provide Random Number Generator API  If you aren t in a multiplatform project  it s better to use the platform api  all the others answers of the question talk about this solution    But if you are in a multiplatform context  the best solution is to implement random by yourself in pure kotlin for share the same random number generator between platforms  It s more simple for dev and testing   To answer to this problem in my personal project  i implement a pure Kotlin Linear Congruential Generator  LCG is the algorithm used by java util Random  Follow this link if you want to use it    https   gist github com 11e5ddb567786af0ed1ae4d7f57441d4  My implementation purpose nextInt range  IntRange  for you      Take care about my purpose  LCG is good for most of the use cases  simulation  games  etc     but is not suitable for cryptographically usage because of the predictability of this method

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Full source code  Can control whether duplicates are allowed   import kotlin math min  abstract class Random        companion object           fun string length  Int  isUnique  Boolean   false   String               if  0    length  return                val alphabet  List lt Char gt      a    z       A    Z       0    9      Add your set here               if  isUnique                    val limit   min length  alphabet count                    val set   mutableSetOf lt Char gt                    do   set add alphabet random      while  set count      limit                  return set joinToString                               return List length    alphabet random     joinToString                        fun alphabet length  Int  isUnique  Boolean   false   String               if  0    length  return                val alphabet     A    Z               if  isUnique                    val limit   min length  alphabet count                    val set   mutableSetOf lt Char gt                    do   set add alphabet random      while  set count      limit                  return set joinToString                                return List length    alphabet random     joinToString

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Kotlin    1 3  multiplatform support for Random  As of 1 3  the standard library provided multi-platform support for randoms  see this answer   Kotlin  lt  1 3 on JavaScript  If you are working with Kotlin JavaScript and don t have access to java util Random  the following will work   fun IntRange random      Math random       endInclusive   1  - start    start  toInt     Used like this      will return an  Int  between 0 and 10  incl    0  10  random

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My suggestion would be an extension function on IntRange to create randoms like this   0  10  random   TL DR Kotlin  gt   1 3  one Random for all platforms As of  1 3  Kotlin comes with its own multi-platform Random generator  It is described in this KEEP  The extension described below is now part of the Kotlin standard library  simply use it like this  val rnds    0  10  random      generated random from 0 to 10 included   Kotlin  lt  1 3 Before 1 3  on the JVM we use Random or even ThreadLocalRandom if we re on JDK  gt  1 6  fun IntRange random             Random   nextInt  endInclusive   1  - start    start  Used like this     will return an  Int  between 0 and 10  incl    0  10  random    If you wanted the function only to return 1  2       9  10 not included   use a range constructed with until   0 until 10  random    If you re working with JDK  gt  1 6  use ThreadLocalRandom current   instead of Random    KotlinJs and other variations For kotlinjs and other use cases which don t allow the usage of java util Random  see this alternative  Also  see this answer for variations of my suggestion  It also includes an extension function for random Chars

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Generate a random integer between from inclusive  and to exclusive   import java util Random  val random   Random    fun rand from  Int  to  Int    Int       return random nextInt to - from    from

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You can create an extension function similar to java util Random nextInt int  but one that takes an IntRange instead of an Int for its bound  fun Random nextInt range  IntRange   Int       return range start   nextInt range last - range start     You can now use this with any Random instance  val random   Random   println random nextInt 5  9      prints 5  6  7  8  or 9  If you don t want to have to manage your own Random instance then you can define a convenience method using  for example  ThreadLocalRandom current    fun rand range  IntRange   Int       return ThreadLocalRandom current   nextInt range     Now you can get a random integer as you would in Ruby without having to first declare a Random instance yourself  rand 5  9     returns 5  6  7  8  or 9

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Using a top-level function  you can achieve exactly the same call syntax as in Ruby  as you wish    fun rand s  Int  e  Int    Random nextInt s  e   1    Usage   rand 1  3     returns either 1  2 or 3

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Whenever there is a situation where you want to generate key or mac address which is hexadecimal number having digits based on user demand  and that too using android and kotlin  then you my below code helps you  private fun getRandomHexString random  SecureRandom  numOfCharsToBePresentInTheHexString  Int   String       val sb   StringBuilder       while  sb length  lt  numOfCharsToBePresentInTheHexString            val randomNumber   random nextInt           val number   String format  quot  08X quot   randomNumber          sb append number            return sb toString

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to be super duper      fun rnd int min  Int  max  Int   Int           var max   max         max -  min         return  Math random       max  toInt     min

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First  you need a RNG  In Kotlin you currently need to use the platform specific ones  there isn t a Kotlin built in one   For the JVM it s java util Random  You ll need to create an instance of it and then call random nextInt n

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Another way of implementing s1m0nw1 s answer would be to access it through a variable  Not that its any more efficient but it saves you from having to type      val ClosedRange lt Int gt  random  Int     get     Random   nextInt  endInclusive   1  - start     start    And now it can be accessed as such   1  10  random

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There is no standard method that does this but you can easily create your own using either Math random   or the class java util Random  Here is an example using the Math random   method   fun random n  Int     Math random     n  toInt   fun random from  Int  to  Int     Math random      to - from    from  toInt   fun random pair  Pair lt Int  Int gt     random pair first  pair second   fun main args  Array lt String gt         val n   10      val rand1   random n      val rand2   random 5  n      val rand3   random 5 to n       println List 10    random n         println List 10    random 5 to n         This is a sample output    9  8  1  7  5  6  9  8  1  9   5  8  9  7  6  6  8  6  7  9

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Building off of  s1m0nw1 excellent answer I made the following changes     0  n  implies inclusive in Kotlin  0 until n  implies exclusive in Kotlin Use a singleton object for the Random instance  optional    Code   private object RandomRangeSingleton   Random    fun ClosedRange lt Int gt  random     RandomRangeSingleton nextInt  endInclusive   1  - start    start   Test Case   fun testRandom             Assert assertTrue                   0  1000  all                        0  5  contains  0  5  random                                        Assert assertTrue                   0  1000  all                        0  4  contains  0 until 5  random                                        Assert assertFalse                   0  1000  all                        0  4  contains  0  5  random

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You could create an extension function   infix fun ClosedRange lt Float gt  step step  Float   Iterable lt Float gt        require start isFinite        require endInclusive isFinite        require step round    gt  0 0     Step must be positive  was   step         require start    endInclusive     Start and endInclusive must not be the same        if  endInclusive  gt  start            return generateSequence start    previous - gt              if  previous    Float POSITIVE INFINITY  return generateSequence null             val next   previous   step round               if  next  gt  endInclusive  null else next round             asIterable              return generateSequence start    previous - gt          if  previous    Float NEGATIVE INFINITY  return generateSequence null         val next   previous - step round           if  next  lt  endInclusive  null else next round         asIterable       Round Float value   fun Float round decimals  Int   DIGITS   Float       var multiplier   1 0f     repeat decimals    multiplier    10       return round this   multiplier    multiplier     Method s usage    0 0f    1 0f  step  1f  forEach   System out println  value   it       Output      value  0 0 value  0 1 value  0 2 value  0 3 value  0 4 value  0 5   value  0 6 value  0 7 value  0 8 value  0 9 value  1 0

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As of kotlin 1 2  you could write     1  3  shuffled   last    Just be aware it s big O n   but for a small list  especially of unique values  it s alright  D

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If the numbers you want to choose from are not consecutive  you can use random     Usage   val list   listOf 3  1  4  5  val number   list random     Returns one of the numbers which are in the list

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Possible Variation to my other answer for random chars  In order to get random Chars  you can define an extension function like this  fun ClosedRange lt Char gt  random    Char            Random   nextInt endInclusive toInt     1 - start toInt      start toInt    toChar       will return a  Char  between A and Z  incl     A    Z   random     If you re working with JDK   1 6  use ThreadLocalRandom current   instead of Random     For kotlinjs and other use cases which don t allow the usage of java util Random  this answer will help   Kotlin    1 3 multiplatform support for Random  As of  1 3  Kotlin comes with its own multiplatform Random generator  It is described in this KEEP  You can now directly use the extension as part of the Kotlin standard library without defining it     a    b   random

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No need to use custom extension functions anymore  IntRange has a random   extension function out-of-the-box now   val randomNumber    0  10  random

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To get a random Int number in Kotlin use the following method    import java util concurrent ThreadLocalRandom  fun randomInt rangeFirstNum Int  rangeLastNum Int        val randomInteger   ThreadLocalRandom current   nextInt rangeFirstNum rangeLastNum      println randomInteger    fun main             randomInt 1 10         Result     random Int numbers from 1 to 9   Hope this helps

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In Kotlin SDK  gt  1 3 you can do it like import kotlin random Random  val number   Random nextInt limit

[random] How can I get a random number in Kotlin?

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