Class Random

java.lang.Object

java.util.Random

All Implemented Interfaces:

Serializable, RandomGenerator

Direct Known Subclasses:

SecureRandom, ThreadLocalRandom

public class Random
extends Object
implements RandomGenerator, Serializable

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 ThreadLocalRandom in multithreaded designs.

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

Since:

1.0

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface RandomGenerator

RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator

Constructor Summary

Constructors

Constructor	Description
Random()	Creates a new random number generator.
Random(long seed)	Creates a new random number generator using a single long seed.

Method Summary

Modifier and Type	Method	Description
DoubleStream	doubles()	Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).
DoubleStream	doubles(double randomNumberOrigin, double randomNumberBound)	Returns an effectively unlimited stream of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).
DoubleStream	doubles(long streamSize)	Returns a stream producing the given streamSize number of pseudorandom double values, each between zero (inclusive) and one (exclusive).
DoubleStream	doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)	Returns a stream producing the given streamSize number of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).
static Random	from(RandomGenerator generator)	Returns an instance of Random that delegates method calls to the RandomGenerator argument.
IntStream	ints()	Returns an effectively unlimited stream of pseudorandom int values.
IntStream	ints(int randomNumberOrigin, int randomNumberBound)	Returns an effectively unlimited stream of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).
IntStream	ints(long streamSize)	Returns a stream producing the given streamSize number of pseudorandom int values.
IntStream	ints(long streamSize, int randomNumberOrigin, int randomNumberBound)	Returns a stream producing the given streamSize number of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).
LongStream	longs()	Returns an effectively unlimited stream of pseudorandom long values.
LongStream	longs(long streamSize)	Returns a stream producing the given streamSize number of pseudorandom long values.
LongStream	longs(long randomNumberOrigin, long randomNumberBound)	Returns an effectively unlimited stream of pseudorandom long values, each conforming to the given origin (inclusive) and bound (exclusive).
LongStream	longs(long streamSize, long randomNumberOrigin, long randomNumberBound)	Returns a stream producing the given streamSize number of pseudorandom long, each conforming to the given origin (inclusive) and bound (exclusive).
protected int	next(int bits)	Generates the next pseudorandom number.
boolean	nextBoolean()	Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence.
void	nextBytes(byte[] bytes)	Generates random bytes and places them into a user-supplied byte array.
double	nextDouble()	Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.
float	nextFloat()	Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.
double	nextGaussian()	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.
int	nextInt()	Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.
int	nextInt(int bound)	Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
long	nextLong()	Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.
void	setSeed(long seed)	Sets or updates the seed of this random number generator using the provided long seed value (optional operation).

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface RandomGenerator

equiDoubles, isDeprecated, nextDouble, nextDouble, nextExponential, nextFloat, nextFloat, nextGaussian, nextInt, nextLong, nextLong

Constructor Details

Random

public 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

public Random(long seed)

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(int).

Parameters:

seed - the initial seed

See Also:

• setSeed(long)

Method Details

from

public static Random from(RandomGenerator generator)

Returns an instance of Random that delegates method calls to the RandomGenerator argument. If the generator is an instance of Random, it is returned. Otherwise, this method returns an instance of Random that delegates all methods except setSeed to the generator. The returned instance's setSeed method always throws UnsupportedOperationException. The returned instance is not serializable.

Parameters:

generator - the RandomGenerator calls are delegated to

Returns:

the delegating Random instance

Throws:

NullPointerException - if generator is null

Since:

19

setSeed

public void setSeed(long seed)

Sets or updates the seed of this random number generator using the provided long seed value (optional operation).

Parameters:

seed - the seed value

Throws:

UnsupportedOperationException - if the setSeed operation is not supported by this random number generator

next

protected int next(int bits)

Generates the next pseudorandom number. This method returns an int value such that, 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.

Parameters:

bits - random bits

Returns:

the next pseudorandom value from this random number generator's sequence

Since:

1.1

nextBytes

public void nextBytes(byte[] bytes)

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.

Specified by:

nextBytes in interface RandomGenerator

Parameters:

bytes - the byte array to fill with random bytes

Throws:

NullPointerException - if the byte array is null

Since:

1.1

nextInt

public int nextInt()

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.

Specified by:

nextInt in interface RandomGenerator

Returns:

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

nextInt

public int nextInt(int bound)

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.

Specified by:

nextInt in interface RandomGenerator

Parameters:

bound - the upper bound (exclusive). Must be positive.

Returns:

the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

Throws:

IllegalArgumentException - if bound is not positive

Since:

1.2

nextLong

public long nextLong()

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.

Specified by:

nextLong in interface RandomGenerator

Returns:

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

nextBoolean

public boolean nextBoolean()

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.

Specified by:

nextBoolean in interface RandomGenerator

Returns:

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

Since:

1.2

nextFloat

public float nextFloat()

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.

Specified by:

nextFloat in interface RandomGenerator

Returns:

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

nextDouble

public double nextDouble()

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.

Specified by:

nextDouble in interface RandomGenerator

Returns:

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

See Also:

• Math.random()

nextGaussian

public double nextGaussian()

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.

Specified by:

nextGaussian in interface RandomGenerator

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

ints

public IntStream ints(long streamSize)

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().

Specified by:

ints in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom int values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

ints

public IntStream ints()

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().

Specified by:

ints in interface RandomGenerator

Returns:

a stream of pseudorandom int values

Since:

1.8

ints

public IntStream ints(long streamSize,
 int randomNumberOrigin,
 int randomNumberBound)

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:

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;
  }
}

Specified by:

ints in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)

Throws:

IllegalArgumentException - if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8

ints

public IntStream ints(int randomNumberOrigin,
 int randomNumberBound)

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:

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;
  }
}

Specified by:

ints in interface RandomGenerator

Parameters:

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)

Throws:

IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8

longs

public LongStream longs(long streamSize)

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().

Specified by:

longs in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

Returns:

a stream of pseudorandom long values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

longs

public LongStream longs()

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().

Specified by:

longs in interface RandomGenerator

Returns:

a stream of pseudorandom long values

Since:

1.8

longs

public LongStream longs(long streamSize,
 long randomNumberOrigin,
 long randomNumberBound)

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:

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;
}

Specified by:

longs in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)

Throws:

IllegalArgumentException - if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8

longs

public LongStream longs(long randomNumberOrigin,
 long randomNumberBound)

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:

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;
}

Specified by:

longs in interface RandomGenerator

Parameters:

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)

Throws:

IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8

doubles

public DoubleStream doubles(long streamSize)

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().

Specified by:

doubles in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

Returns:

a stream of double values

Throws:

IllegalArgumentException - if streamSize is less than zero

Since:

1.8

doubles

public DoubleStream doubles()

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().

Specified by:

doubles in interface RandomGenerator

Returns:

a stream of pseudorandom double values

Since:

1.8

doubles

public DoubleStream doubles(long streamSize,
 double randomNumberOrigin,
 double randomNumberBound)

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

Specified by:

doubles in interface RandomGenerator

Parameters:

streamSize - the number of values to generate

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)

Throws:

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

Since:

1.8

doubles

public DoubleStream doubles(double randomNumberOrigin,
 double randomNumberBound)

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

Specified by:

doubles in interface RandomGenerator

Parameters:

randomNumberOrigin - the origin (inclusive) of each random value

randomNumberBound - the bound (exclusive) of each random value

Returns:

a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)

Throws:

IllegalArgumentException - if randomNumberOrigin is not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound

Since:

1.8