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 | |
|---|---|
Random()Creates a new random number generator. |
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Creates a new random number generator using a single |
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| Public methods | |
|---|---|
| open DoubleStream! |
Returns a stream producing the given |
| open DoubleStream! |
doubles()Returns an effectively unlimited stream of pseudorandom |
| open DoubleStream! |
Returns a stream producing the given |
| open DoubleStream! |
Returns an effectively unlimited stream of pseudorandom |
| open IntStream! |
Returns a stream producing the given |
| open IntStream! |
ints()Returns an effectively unlimited stream of pseudorandom |
| open IntStream! |
Returns a stream producing the given |
| open IntStream! |
Returns an effectively unlimited stream of pseudorandom |
| open LongStream! |
Returns a stream producing the given |
| open LongStream! |
longs()Returns an effectively unlimited stream of pseudorandom |
| open LongStream! |
Returns a stream producing the given |
| open LongStream! |
Returns an effectively unlimited stream of pseudorandom |
| open Boolean |
Returns the next pseudorandom, uniformly distributed |
| open Unit |
Generates random bytes and places them into a user-supplied byte array. |
| open Double |
Returns the next pseudorandom, uniformly distributed |
| open Float |
Returns the next pseudorandom, uniformly distributed |
| open Double |
Returns the next pseudorandom, Gaussian ("normally") distributed |
| open Int |
nextInt()Returns the next pseudorandom, uniformly distributed |
| open Int |
Returns a pseudorandom, uniformly distributed |
| open Long |
nextLong()Returns the next pseudorandom, uniformly distributed |
| open Unit |
Sets the seed of this random number generator using a single |
| Protected methods | |
|---|---|
| open Int |
Generates the next pseudorandom number. |
| Inherited functions | |
|---|---|
Public constructors
Random
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
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
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
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
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 >= 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
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 >= 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
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
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
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 > 0) {
return nextInt(n) + origin;
}
else { // range not representable as int
int r;
do {
r = nextInt();
} while (r < origin || r >= 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
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 > 0) {
return nextInt(n) + origin;
}
else { // range not representable as int
int r;
do {
r = nextInt();
} while (r < origin || r >= 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
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
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
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 & m) == 0L) // power of two
r = (r & m) + origin;
else if (n > 0L) { // reject over-represented candidates
for (long u = r >>> 1; // ensure nonnegative
u + m - (r = u % n) < 0L; // rejection check
u = nextLong() >>> 1) // retry
;
r += origin;
}
else { // range not representable as long
while (r < origin || r >= 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
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 & m) == 0L) // power of two
r = (r & m) + origin;
else if (n > 0L) { // reject over-represented candidates
for (long u = r >>> 1; // ensure nonnegative
u + m - (r = u % n) < 0L; // rejection check
u = nextLong() >>> 1) // retry
;
r += origin;
}
else { // range not representable as long
while (r < origin || r >= 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
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
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
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 |
See Also
nextFloat
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
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
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
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
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
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) & ((1L << 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
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) & ((1L << 48) - 1)</code>and returning
<code>(int)(seed >>> (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 |