Serializable
, RandomGenerator
SecureRandom
, ThreadLocalRandom
An instance of this class is used to generate a stream of pseudorandom numbers; its period is only 2
48. 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.
Constructors
Creates a new random number generator.
Creates a new random number generator using a single long
seed.
Returns an effectively unlimited stream of pseudorandom double
values, each between zero (inclusive) and one (exclusive).
doubles(double randomNumberOrigin, double randomNumberBound)
Returns an effectively unlimited stream of pseudorandom double
values, each conforming to the given origin (inclusive) and bound (exclusive).
Returns a stream producing the given streamSize
number of pseudorandom double
values, each between zero (inclusive) and one (exclusive).
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).
Returns an instance of
Random
that delegates method calls to the
RandomGenerator
argument.
Returns an effectively unlimited stream of pseudorandom int
values.
ints(int randomNumberOrigin, int randomNumberBound)
Returns an effectively unlimited stream of pseudorandom int
values, each conforming to the given origin (inclusive) and bound (exclusive).
Returns a stream producing the given streamSize
number of pseudorandom int
values.
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).
Returns an effectively unlimited stream of pseudorandom long
values.
Returns a stream producing the given streamSize
number of pseudorandom long
values.
longs(long randomNumberOrigin, long randomNumberBound)
Returns an effectively unlimited stream of pseudorandom long
values, each conforming to the given origin (inclusive) and bound (exclusive).
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
Generates the next pseudorandom number.
boolean
Returns the next pseudorandom, uniformly distributed boolean
value from this random number generator's sequence.
void
Generates random bytes and places them into a user-supplied byte array.
double
Returns the next pseudorandom, uniformly distributed double
value between 0.0
and 1.0
from this random number generator's sequence.
float
Returns the next pseudorandom, uniformly distributed float
value between 0.0
and 1.0
from this random number generator's sequence.
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.
int
Returns the next pseudorandom, uniformly distributed int
value from this random number generator's sequence.
int
Returns a pseudorandom, uniformly distributed int
value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
long
Returns the next pseudorandom, uniformly distributed long
value from this random number generator's sequence.
void
Sets or updates the seed of this random number generator using the provided long
seed value (optional operation).
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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.
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)
.
new Random(seed)
is equivalent to:
Random rnd = new Random();
rnd.setSeed(seed);
seed
- the initial seed
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.
generator
- the RandomGenerator
calls are delegated to
Random
instance
NullPointerException
- if generator is null
public void setSeed(long seed)
Sets or updates the seed of this random number generator using the provided long
seed value (optional operation).
new Random(seed)
. It atomically updates the seed to
(seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)
and clears the haveNextNextGaussian
flag used by nextGaussian()
. Note that this uses only 48 bits of the given seed value.
seed
- the seed value
UnsupportedOperationException
- if the setSeed
operation is not supported by this random number generator
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
.
(seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)
and returns
(int)(seed >>> (48 - bits))
.
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.
bits
- random bits
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.
nextBytes
in interface RandomGenerator
nextBytes
is implemented by class Random
as if by:
public void nextBytes(byte[] bytes) {
for (int i = 0; i < bytes.length; )
for (int rnd = nextInt(), n = Math.min(bytes.length - i, 4);
n-- > 0; rnd >>= 8)
bytes[i++] = (byte)rnd;
}
bytes
- the byte array to fill with random bytes
NullPointerException
- if the byte array is null
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.
nextInt
in interface RandomGenerator
nextInt
is implemented by class Random
as if by:
public int nextInt() {
return next(32);
}
int
value from this random number generator's sequence
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.
nextInt
in interface RandomGenerator
nextInt(int bound)
is implemented by class Random
as if by:
public int nextInt(int bound) {
if (bound <= 0)
throw new IllegalArgumentException("bound must be positive");
if ((bound & -bound) == bound) // i.e., bound is a power of 2
return (int)((bound * (long)next(31)) >> 31);
int bits, val;
do {
bits = next(31);
val = bits % bound;
} while (bits - val + (bound-1) < 0);
return val;
}
The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose int
values from the stated range with perfect uniformity.
The algorithm is slightly tricky. It rejects values that would result in an uneven distribution (due to the fact that 2^31 is not divisible by n). The probability of a value being rejected depends on n. The worst case is n=2^30+1, for which the probability of a reject is 1/2, and the expected number of iterations before the loop terminates is 2.
The algorithm treats the case where n is a power of two specially: it returns the correct number of high-order bits from the underlying pseudo-random number generator. In the absence of special treatment, the correct number of low-order bits would be returned. Linear congruential pseudo-random number generators such as the one implemented by this class are known to have short periods in the sequence of values of their low-order bits. Thus, this special case greatly increases the length of the sequence of values returned by successive calls to this method if n is a small power of two.
bound
- the upper bound (exclusive). Must be positive.
int
value between zero (inclusive) and bound
(exclusive) from this random number generator's sequence
IllegalArgumentException
- if bound is not positive
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.
nextLong
in interface RandomGenerator
nextLong
is implemented by class Random
as if by:
public long nextLong() {
return ((long)next(32) << 32) + next(32);
}
Because class Random
uses a seed with only 48 bits, this algorithm will not return all possible long
values.
long
value from this random number generator's sequence
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.
nextBoolean
in interface RandomGenerator
nextBoolean
is implemented by class Random
as if by:
public boolean nextBoolean() {
return next(1) != 0;
}
boolean
value from this random number generator's sequence
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.
nextFloat
in interface RandomGenerator
nextFloat
is implemented by class Random
as if by:
public float nextFloat() {
return next(24) / ((float)(1 << 24));
}
The hedge "approximately" is used in the foregoing description only because the next method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose float
values from the stated range with perfect uniformity.
[In early versions of Java, the result was incorrectly calculated as:
return next(30) / ((float)(1 << 30));
This might seem to be equivalent, if not better, but in fact it introduced a slight nonuniformity because of the bias in the rounding of floating-point numbers: it was slightly more likely that the low-order bit of the significand would be 0 than that it would be 1.]
float
value between 0.0f
and 1.0f
from this random number generator's sequence
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.
nextDouble
in interface RandomGenerator
nextDouble
is implemented by class Random
as if by:
public double nextDouble() {
return (((long)next(26) << 27) + next(27))
/ (double)(1L << 53);
}
The hedge "approximately" is used in the foregoing description only because the next
method is only approximately an unbiased source of independently chosen bits. If it were a perfect source of randomly chosen bits, then the algorithm shown would choose double
values from the stated range with perfect uniformity.
[In early versions of Java, the result was incorrectly calculated as:
return (((long)next(27) << 27) + next(27)) / (double)(1L << 54);
This might seem to be equivalent, if not better, but in fact it introduced a large nonuniformity because of the bias in the rounding of floating-point numbers: it was three times as likely that the low-order bit of the significand would be 0 than that it would be 1! This nonuniformity probably doesn't matter much in practice, but we strive for perfection.]
double
value between 0.0
and 1.0
from this random number generator's sequence
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.
nextGaussian
in interface RandomGenerator
nextGaussian
is implemented by class Random
as if by a threadsafe version of the following:
private double nextNextGaussian;
private boolean haveNextNextGaussian = false;
public double nextGaussian() {
if (haveNextNextGaussian) {
haveNextNextGaussian = false;
return nextNextGaussian;
} else {
double v1, v2, s;
do {
v1 = 2 * nextDouble() - 1; // between -1.0 and 1.0
v2 = 2 * nextDouble() - 1; // between -1.0 and 1.0
s = v1 * v1 + v2 * v2;
} while (s >= 1 || s == 0);
double multiplier = StrictMath.sqrt(-2 * StrictMath.log(s)/s);
nextNextGaussian = v2 * multiplier;
haveNextNextGaussian = true;
return v1 * multiplier;
}
}
This uses the polar method of G. E. P. Box, M. E. Muller, and G. Marsaglia, as described by Donald E. Knuth in The Art of Computer Programming, Volume 2, third edition: Seminumerical Algorithms, section 3.4.1, subsection C, algorithm P. Note that it generates two independent values at the cost of only one call to StrictMath.log
and one call to StrictMath.sqrt
.
double
value with mean 0.0
and standard deviation 1.0
from this random number generator's sequence
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()
.
ints
in interface RandomGenerator
streamSize
- the number of values to generate
int
values
IllegalArgumentException
- if streamSize
is less than zero
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()
.
ints
in interface RandomGenerator
ints(Long.MAX_VALUE)
.
int
values
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;
}
}
ints
in interface RandomGenerator
streamSize
- the number of values to generate
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
int
values, each with the given origin (inclusive) and bound (exclusive)
IllegalArgumentException
- if streamSize
is less than zero, or randomNumberOrigin
is greater than or equal to 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;
}
}
ints
in interface RandomGenerator
ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
int
values, each with the given origin (inclusive) and bound (exclusive)
IllegalArgumentException
- if randomNumberOrigin
is greater than or equal to randomNumberBound
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()
.
longs
in interface RandomGenerator
streamSize
- the number of values to generate
long
values
IllegalArgumentException
- if streamSize
is less than zero
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()
.
longs
in interface RandomGenerator
longs(Long.MAX_VALUE)
.
long
values
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;
}
longs
in interface RandomGenerator
streamSize
- the number of values to generate
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
long
values, each with the given origin (inclusive) and bound (exclusive)
IllegalArgumentException
- if streamSize
is less than zero, or randomNumberOrigin
is greater than or equal to 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;
}
longs
in interface RandomGenerator
longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
long
values, each with the given origin (inclusive) and bound (exclusive)
IllegalArgumentException
- if randomNumberOrigin
is greater than or equal to randomNumberBound
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()
.
doubles
in interface RandomGenerator
streamSize
- the number of values to generate
double
values
IllegalArgumentException
- if streamSize
is less than zero
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()
.
doubles
in interface RandomGenerator
doubles(Long.MAX_VALUE)
.
double
values
Returns a stream producing the given streamSize
number of pseudorandom double
values, each conforming to the given origin (inclusive) and bound (exclusive).
doubles
in interface RandomGenerator
streamSize
- the number of values to generate
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
double
values, each with the given origin (inclusive) and bound (exclusive)
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
Returns an effectively unlimited stream of pseudorandom double
values, each conforming to the given origin (inclusive) and bound (exclusive).
doubles
in interface RandomGenerator
doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)
.
randomNumberOrigin
- the origin (inclusive) of each random value
randomNumberBound
- the bound (exclusive) of each random value
double
values, each with the given origin (inclusive) and bound (exclusive)
IllegalArgumentException
- if randomNumberOrigin
is not finite, or randomNumberBound
is not finite, or randomNumberOrigin
is greater than or equal to randomNumberBound
RetroSearch is an open source project built by @garambo | Open a GitHub Issue
Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo
HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4