Added in API level 1

Random

open class Random : RandomGenerator, Serializable
kotlin.Any
   ↳ java.util.Random

An instance of this class is used to generate a stream of pseudorandom numbers; its period is only 248. The class uses a 48-bit seed, which is modified using a linear congruential formula. (See Donald E. Knuth, The Art of Computer Programming, Volume 2, Third edition: Seminumerical Algorithms, Section 3.2.1.)

If two instances of Random are created with the same seed, and the same sequence of method calls is made for each, they will generate and return identical sequences of numbers. In order to guarantee this property, particular algorithms are specified for the class Random. Java implementations must use all the algorithms shown here for the class Random, for the sake of absolute portability of Java code. However, subclasses of class Random are permitted to use other algorithms, so long as they adhere to the general contracts for all the methods.

The algorithms implemented by class Random use a protected utility method that on each invocation can supply up to 32 pseudorandomly generated bits.

Many applications will find the method Math#random simpler to use.

Instances of java.util.Random are threadsafe. However, the concurrent use of the same java.util.Random instance across threads may encounter contention and consequent poor performance. Consider instead using java.util.concurrent.ThreadLocalRandom in multithreaded designs.

Instances of java.util.Random are not cryptographically secure. Consider instead using java.security.SecureRandom to get a cryptographically secure pseudo-random number generator for use by security-sensitive applications.

Summary

Public constructors

Creates a new random number generator.

Random(seed: Long)

Creates a new random number generator using a single long seed.

Public methods
open DoubleStream!
doubles(streamSize: Long)

Returns a stream producing the given streamSize number of pseudorandom double values, each between zero (inclusive) and one (exclusive).

open DoubleStream!

Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).

open DoubleStream!
doubles(streamSize: Long, randomNumberOrigin: Double, randomNumberBound: Double)

Returns a stream producing the given streamSize number of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).

open DoubleStream!
doubles(randomNumberOrigin: Double, randomNumberBound: Double)

Returns an effectively unlimited stream of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).

open IntStream!
ints(streamSize: Long)

Returns a stream producing the given streamSize number of pseudorandom int values.

open IntStream!

Returns an effectively unlimited stream of pseudorandom int values.

open IntStream!
ints(streamSize: Long, randomNumberOrigin: Int, randomNumberBound: Int)

Returns a stream producing the given streamSize number of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).

open IntStream!
ints(randomNumberOrigin: Int, randomNumberBound: Int)

Returns an effectively unlimited stream of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).

open LongStream!
longs(streamSize: Long)

Returns a stream producing the given streamSize number of pseudorandom long values.

open LongStream!

Returns an effectively unlimited stream of pseudorandom long values.

open LongStream!
longs(streamSize: Long, randomNumberOrigin: Long, randomNumberBound: Long)

Returns a stream producing the given streamSize number of pseudorandom long, each conforming to the given origin (inclusive) and bound (exclusive).

open LongStream!
longs(randomNumberOrigin: Long, randomNumberBound: Long)

Returns an effectively unlimited stream of pseudorandom long values, each conforming to the given origin (inclusive) and bound (exclusive).

open Boolean

Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence.

open Unit

Generates random bytes and places them into a user-supplied byte array.

open Double

Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.

open Float

Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.

open Double

Returns the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.

open Int

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.

open Int
nextInt(bound: Int)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.

open Long

Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.

open Unit
setSeed(seed: Long)

Sets the seed of this random number generator using a single long seed.

Protected methods
open Int
next(bits: Int)

Generates the next pseudorandom number.

Inherited functions

Public constructors

Random

Added in API level 1
Random()

Creates a new random number generator. This constructor sets the seed of the random number generator to a value very likely to be distinct from any other invocation of this constructor.

Random

Added in API level 1
Random(seed: Long)

Creates a new random number generator using a single long seed. The seed is the initial value of the internal state of the pseudorandom number generator which is maintained by method next.

Parameters
seed Long: the initial seed

See Also

Public methods

doubles

Added in API level 24
open fun doubles(streamSize: Long): DoubleStream!

Returns a stream producing the given streamSize number of pseudorandom double values, each between zero (inclusive) and one (exclusive).

A pseudorandom double value is generated as if it's the result of calling the method nextDouble().

Parameters
streamSize Long: the number of values to generate
Return
DoubleStream! a stream of double values
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero

doubles

Added in API level 24
open fun doubles(): DoubleStream!

Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).

A pseudorandom double value is generated as if it's the result of calling the method nextDouble().

Return
DoubleStream! a stream of pseudorandom double values

doubles

Added in API level 24
open fun doubles(
    streamSize: Long,
    randomNumberOrigin: Double,
    randomNumberBound: Double
): DoubleStream!

Returns a stream producing the given streamSize number of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom double value is generated as if it's the result of calling the following method with the origin and bound:

<code>double nextDouble(double origin, double bound) {
    double r = nextDouble();
    r = r * (bound - origin) + origin;
    if (r &gt;= bound) // correct for rounding
      r = Math.nextDown(bound);
    return r;
  }</code>
Parameters
streamSize Long: the number of values to generate
randomNumberOrigin Double: the origin (inclusive) of each random value
randomNumberBound Double: the bound (exclusive) of each random value
Return
DoubleStream! a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero, or randomNumberOrigin is not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound

doubles

Added in API level 24
open fun doubles(
    randomNumberOrigin: Double,
    randomNumberBound: Double
): DoubleStream!

Returns an effectively unlimited stream of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom double value is generated as if it's the result of calling the following method with the origin and bound:

<code>double nextDouble(double origin, double bound) {
    double r = nextDouble();
    r = r * (bound - origin) + origin;
    if (r &gt;= bound) // correct for rounding
      r = Math.nextDown(bound);
    return r;
  }</code>
Parameters
randomNumberOrigin Double: the origin (inclusive) of each random value
randomNumberBound Double: the bound (exclusive) of each random value
Return
DoubleStream! a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if randomNumberOrigin is greater than or equal to randomNumberBound

ints

Added in API level 24
open fun ints(streamSize: Long): IntStream!

Returns a stream producing the given streamSize number of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method nextInt().

Parameters
streamSize Long: the number of values to generate
Return
IntStream! a stream of pseudorandom int values
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero

ints

Added in API level 24
open fun ints(): IntStream!

Returns an effectively unlimited stream of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method nextInt().

Return
IntStream! a stream of pseudorandom int values

ints

Added in API level 24
open fun ints(
    streamSize: Long,
    randomNumberOrigin: Int,
    randomNumberBound: Int
): IntStream!

Returns a stream producing the given streamSize number of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

<code>int nextInt(int origin, int bound) {
    int n = bound - origin;
    if (n &gt; 0) {
      return nextInt(n) + origin;
    }
    else {  // range not representable as int
      int r;
      do {
        r = nextInt();
      } while (r &lt; origin || r &gt;= bound);
      return r;
    }
  }</code>
Parameters
streamSize Long: the number of values to generate
randomNumberOrigin Int: the origin (inclusive) of each random value
randomNumberBound Int: the bound (exclusive) of each random value
Return
IntStream! a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound

ints

Added in API level 24
open fun ints(
    randomNumberOrigin: Int,
    randomNumberBound: Int
): IntStream!

Returns an effectively unlimited stream of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

<code>int nextInt(int origin, int bound) {
    int n = bound - origin;
    if (n &gt; 0) {
      return nextInt(n) + origin;
    }
    else {  // range not representable as int
      int r;
      do {
        r = nextInt();
      } while (r &lt; origin || r &gt;= bound);
      return r;
    }
  }</code>
Parameters
randomNumberOrigin Int: the origin (inclusive) of each random value
randomNumberBound Int: the bound (exclusive) of each random value
Return
IntStream! a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if randomNumberOrigin is greater than or equal to randomNumberBound

longs

Added in API level 24
open fun longs(streamSize: Long): LongStream!

Returns a stream producing the given streamSize number of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method nextLong().

Parameters
streamSize Long: the number of values to generate
Return
LongStream! a stream of pseudorandom long values
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero

longs

Added in API level 24
open fun longs(): LongStream!

Returns an effectively unlimited stream of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method nextLong().

Return
LongStream! a stream of pseudorandom long values

longs

Added in API level 24
open fun longs(
    streamSize: Long,
    randomNumberOrigin: Long,
    randomNumberBound: Long
): LongStream!

Returns a stream producing the given streamSize number of pseudorandom long, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

<code>long nextLong(long origin, long bound) {
    long r = nextLong();
    long n = bound - origin, m = n - 1;
    if ((n &amp; m) == 0L)  // power of two
      r = (r &amp; m) + origin;
    else if (n &gt; 0L) {  // reject over-represented candidates
      for (long u = r &gt;&gt;&gt; 1;            // ensure nonnegative
           u + m - (r = u % n) &lt; 0L;    // rejection check
           u = nextLong() &gt;&gt;&gt; 1) // retry
          ;
      r += origin;
    }
    else {              // range not representable as long
      while (r &lt; origin || r &gt;= bound)
        r = nextLong();
    }
    return r;
  }</code>
Parameters
streamSize Long: the number of values to generate
randomNumberOrigin Long: the origin (inclusive) of each random value
randomNumberBound Long: the bound (exclusive) of each random value
Return
LongStream! a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound

longs

Added in API level 24
open fun longs(
    randomNumberOrigin: Long,
    randomNumberBound: Long
): LongStream!

Returns an effectively unlimited stream of pseudorandom long values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

<code>long nextLong(long origin, long bound) {
    long r = nextLong();
    long n = bound - origin, m = n - 1;
    if ((n &amp; m) == 0L)  // power of two
      r = (r &amp; m) + origin;
    else if (n &gt; 0L) {  // reject over-represented candidates
      for (long u = r &gt;&gt;&gt; 1;            // ensure nonnegative
           u + m - (r = u % n) &lt; 0L;    // rejection check
           u = nextLong() &gt;&gt;&gt; 1) // retry
          ;
      r += origin;
    }
    else {              // range not representable as long
      while (r &lt; origin || r &gt;= bound)
        r = nextLong();
    }
    return r;
  }</code>
Parameters
randomNumberOrigin Long: the origin (inclusive) of each random value
randomNumberBound Long: the bound (exclusive) of each random value
Return
LongStream! a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)
Exceptions
java.lang.IllegalArgumentException if randomNumberOrigin is greater than or equal to randomNumberBound

nextBoolean

Added in API level 1
open fun nextBoolean(): Boolean

Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence. The general contract of nextBoolean is that one boolean value is pseudorandomly generated and returned. The values true and false are produced with (approximately) equal probability.

Return
Boolean the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence

nextBytes

Added in API level 1
open fun nextBytes(bytes: ByteArray!): Unit

Generates random bytes and places them into a user-supplied byte array. The number of random bytes produced is equal to the length of the byte array.

Parameters
bytes ByteArray!: the byte array to fill with random bytes
Exceptions
java.lang.NullPointerException if the byte array is null

nextDouble

Added in API level 1
open fun nextDouble(): Double

Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextDouble is that one double value, chosen (approximately) uniformly from the range 0.0d (inclusive) to 1.0d (exclusive), is pseudorandomly generated and returned.

Return
Double the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence

nextFloat

Added in API level 1
open fun nextFloat(): Float

Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextFloat is that one float value, chosen (approximately) uniformly from the range 0.0f (inclusive) to 1.0f (exclusive), is pseudorandomly generated and returned. All 224 possible float values of the form m x 2-24, where m is a positive integer less than 224, are produced with (approximately) equal probability.

Return
Float the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence

nextGaussian

Added in API level 1
open fun nextGaussian(): Double

Returns the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.

The general contract of nextGaussian is that one double value, chosen from (approximately) the usual normal distribution with mean 0.0 and standard deviation 1.0, is pseudorandomly generated and returned.

Return
Double the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence

nextInt

Added in API level 1
open fun nextInt(): Int

Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence. The general contract of nextInt is that one int value is pseudorandomly generated and returned. All 232 possible int values are produced with (approximately) equal probability.

Return
Int the next pseudorandom, uniformly distributed int value from this random number generator's sequence

nextInt

Added in API level 1
open fun nextInt(bound: Int): Int

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.

Parameters
bound Int: the upper bound (exclusive). Must be positive.
Return
Int the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence
Exceptions
java.lang.IllegalArgumentException if bound is not positive

nextLong

Added in API level 1
open fun nextLong(): Long

Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence. The general contract of nextLong is that one long value is pseudorandomly generated and returned.

Return
Long the next pseudorandom, uniformly distributed long value from this random number generator's sequence

setSeed

Added in API level 1
open fun setSeed(seed: Long): Unit

Sets the seed of this random number generator using a single long seed. The general contract of setSeed is that it alters the state of this random number generator object so as to be in exactly the same state as if it had just been created with the argument seed as a seed. The method setSeed is implemented by class Random by atomically updating the seed to

<code>(seed ^ 0x5DEECE66DL) &amp; ((1L &lt;&lt; 48) - 1)</code>
and clearing the haveNextNextGaussian flag used by #nextGaussian.

The implementation of setSeed by class Random happens to use only 48 bits of the given seed. In general, however, an overriding method may use all 64 bits of the long argument as a seed value.

Parameters
seed Long: the initial seed

Protected methods

next

Added in API level 1
protected open fun next(bits: Int): Int

Generates the next pseudorandom number. Subclasses should override this, as this is used by all other methods.

The general contract of next is that it returns an int value and if the argument bits is between 1 and 32 (inclusive), then that many low-order bits of the returned value will be (approximately) independently chosen bit values, each of which is (approximately) equally likely to be 0 or 1. The method next is implemented by class Random by atomically updating the seed to

<code>(seed * 0x5DEECE66DL + 0xBL) &amp; ((1L &lt;&lt; 48) - 1)</code>
and returning
<code>(int)(seed &gt;&gt;&gt; (48 - bits))</code>.
This is a linear congruential pseudorandom number generator, as defined by D. H. Lehmer and described by Donald E. Knuth in The Art of Computer Programming, Volume 2, Third edition: Seminumerical Algorithms, section 3.2.1.
Parameters
bits Int: random bits
Return
Int the next pseudorandom value from this random number generator's sequence