* If two instances of {@code 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 {@code Random}. Java implementations must use all the algorithms * shown here for the class {@code Random}, for the sake of absolute * portability of Java code. However, subclasses of class {@code 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 {@code Random} use a * {@code protected} utility method that on each invocation can supply * up to 32 pseudorandomly generated bits. *
* Many applications will find the method {@link Math#random} simpler to use. * *
Instances of {@code java.util.Random} are threadsafe. * However, the concurrent use of the same {@code java.util.Random} * instance across threads may encounter contention and consequent * poor performance. Consider instead using * {@link java.util.concurrent.ThreadLocalRandom} in multithreaded * designs. * *
Instances of {@code java.util.Random} are not cryptographically * secure. Consider instead using {@link java.security.SecureRandom} to * get a cryptographically secure pseudo-random number generator for use * by security-sensitive applications. * * @author Frank Yellin * @since 1.0 */ public class Random implements java.io.Serializable { /** use serialVersionUID from JDK 1.1 for interoperability */ static final long serialVersionUID = 3905348978240129619L; /** * The internal state associated with this pseudorandom number generator. * (The specs for the methods in this class describe the ongoing * computation of this value.) */ private final AtomicLong seed; private static final long multiplier = 0x5DEECE66DL; private static final long addend = 0xBL; private static final long mask = (1L << 48) - 1; private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53) // IllegalArgumentException messages static final String BadBound = "bound must be positive"; static final String BadRange = "bound must be greater than origin"; static final String BadSize = "size must be non-negative"; /** * 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() { this(seedUniquifier() ^ System.nanoTime()); } private static long seedUniquifier() { // L'Ecuyer, "Tables of Linear Congruential Generators of // Different Sizes and Good Lattice Structure", 1999 for (;;) { long current = seedUniquifier.get(); long next = current * 181783497276652981L; if (seedUniquifier.compareAndSet(current, next)) return next; } } private static final AtomicLong seedUniquifier = new AtomicLong(8682522807148012L); /** * Creates a new random number generator using a single {@code long} seed. * The seed is the initial value of the internal state of the pseudorandom * number generator which is maintained by method {@link #next}. * *
The invocation {@code new Random(seed)} is equivalent to: *
{@code
* Random rnd = new Random();
* rnd.setSeed(seed);}
*
* @param seed the initial seed
* @see #setSeed(long)
*/
public Random(long seed) {
if (getClass() == Random.class)
this.seed = new AtomicLong(initialScramble(seed));
else {
// subclass might have overriden setSeed
this.seed = new AtomicLong();
setSeed(seed);
}
}
private static long initialScramble(long seed) {
return (seed ^ multiplier) & mask;
}
/**
* Sets the seed of this random number generator using a single
* {@code long} seed. The general contract of {@code 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 {@code seed} as a seed. The method
* {@code setSeed} is implemented by class {@code Random} by
* atomically updating the seed to
* {@code (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)}
* and clearing the {@code haveNextNextGaussian} flag used by {@link
* #nextGaussian}.
*
* The implementation of {@code setSeed} by class {@code Random} * happens to use only 48 bits of the given seed. In general, however, * an overriding method may use all 64 bits of the {@code long} * argument as a seed value. * * @param seed the initial seed */ synchronized public void setSeed(long seed) { this.seed.set(initialScramble(seed)); haveNextNextGaussian = false; } /** * Generates the next pseudorandom number. Subclasses should * override this, as this is used by all other methods. * *
The general contract of {@code next} is that it returns an * {@code int} value and if the argument {@code bits} is between * {@code 1} and {@code 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 {@code 0} or {@code 1}. The method {@code next} is * implemented by class {@code Random} by atomically updating the seed to *
{@code (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)}
* and returning
* {@code (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 3:
* Seminumerical Algorithms, section 3.2.1.
*
* @param bits random bits
* @return the next pseudorandom value from this random number
* generator's sequence
* @since 1.1
*/
protected int next(int bits) {
long oldseed, nextseed;
AtomicLong seed = this.seed;
do {
oldseed = seed.get();
nextseed = (oldseed * multiplier + addend) & mask;
} while (!seed.compareAndSet(oldseed, nextseed));
return (int)(nextseed >>> (48 - bits));
}
/**
* 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.
*
* The method {@code nextBytes} is implemented by class {@code Random} * as if by: *
{@code
* 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;
* }}
*
* @param bytes the byte array to fill with random bytes
* @throws NullPointerException if the byte array is null
* @since 1.1
*/
public void nextBytes(byte[] bytes) {
for (int i = 0, len = bytes.length; i < len; )
for (int rnd = nextInt(),
n = Math.min(len - i, Integer.SIZE/Byte.SIZE);
n-- > 0; rnd >>= Byte.SIZE)
bytes[i++] = (byte)rnd;
}
/**
* The form of nextLong used by LongStream Spliterators. If
* origin is greater than bound, acts as unbounded form of
* nextLong, else as bounded form.
*
* @param origin the least value, unless greater than bound
* @param bound the upper bound (exclusive), must not equal origin
* @return a pseudorandom value
*/
final long internalNextLong(long origin, long bound) {
long r = nextLong();
if (origin < bound) {
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;
}
/**
* The form of nextInt used by IntStream Spliterators.
* For the unbounded case: uses nextInt().
* For the bounded case with representable range: uses nextInt(int bound)
* For the bounded case with unrepresentable range: uses nextInt()
*
* @param origin the least value, unless greater than bound
* @param bound the upper bound (exclusive), must not equal origin
* @return a pseudorandom value
*/
final int internalNextInt(int origin, int bound) {
if (origin < 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;
}
}
else {
return nextInt();
}
}
/**
* The form of nextDouble used by DoubleStream Spliterators.
*
* @param origin the least value, unless greater than bound
* @param bound the upper bound (exclusive), must not equal origin
* @return a pseudorandom value
*/
final double internalNextDouble(double origin, double bound) {
double r = nextDouble();
if (origin < bound) {
r = r * (bound - origin) + origin;
if (r >= bound) // correct for rounding
r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
}
return r;
}
/**
* Returns the next pseudorandom, uniformly distributed {@code int}
* value from this random number generator's sequence. The general
* contract of {@code nextInt} is that one {@code int} value is
* pseudorandomly generated and returned. All 232 possible
* {@code int} values are produced with (approximately) equal probability.
*
* The method {@code nextInt} is implemented by class {@code Random} * as if by: *
{@code
* public int nextInt() {
* return next(32);
* }}
*
* @return the next pseudorandom, uniformly distributed {@code int}
* value from this random number generator's sequence
*/
public int nextInt() {
return next(32);
}
/**
* Returns a pseudorandom, uniformly distributed {@code int} value
* between 0 (inclusive) and the specified value (exclusive), drawn from
* this random number generator's sequence. The general contract of
* {@code nextInt} is that one {@code int} value in the specified range
* is pseudorandomly generated and returned. All {@code bound} possible
* {@code int} values are produced with (approximately) equal
* probability. The method {@code nextInt(int bound)} is implemented by
* class {@code Random} as if by:
* {@code
* 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 {@code 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. * * @param bound the upper bound (exclusive). Must be positive. * @return the next pseudorandom, uniformly distributed {@code int} * value between zero (inclusive) and {@code bound} (exclusive) * from this random number generator's sequence * @throws IllegalArgumentException if bound is not positive * @since 1.2 */ public int nextInt(int bound) { if (bound <= 0) throw new IllegalArgumentException(BadBound); int r = next(31); int m = bound - 1; if ((bound & m) == 0) // i.e., bound is a power of 2 r = (int)((bound * (long)r) >> 31); else { for (int u = r; u - (r = u % bound) + m < 0; u = next(31)) ; } return r; } /** * Returns the next pseudorandom, uniformly distributed {@code long} * value from this random number generator's sequence. The general * contract of {@code nextLong} is that one {@code long} value is * pseudorandomly generated and returned. * *
The method {@code nextLong} is implemented by class {@code Random} * as if by: *
{@code
* public long nextLong() {
* return ((long)next(32) << 32) + next(32);
* }}
*
* Because class {@code Random} uses a seed with only 48 bits,
* this algorithm will not return all possible {@code long} values.
*
* @return the next pseudorandom, uniformly distributed {@code long}
* value from this random number generator's sequence
*/
public long nextLong() {
// it's okay that the bottom word remains signed.
return ((long)(next(32)) << 32) + next(32);
}
/**
* Returns the next pseudorandom, uniformly distributed
* {@code boolean} value from this random number generator's
* sequence. The general contract of {@code nextBoolean} is that one
* {@code boolean} value is pseudorandomly generated and returned. The
* values {@code true} and {@code false} are produced with
* (approximately) equal probability.
*
* The method {@code nextBoolean} is implemented by class {@code Random} * as if by: *
{@code
* public boolean nextBoolean() {
* return next(1) != 0;
* }}
*
* @return the next pseudorandom, uniformly distributed
* {@code boolean} value from this random number generator's
* sequence
* @since 1.2
*/
public boolean nextBoolean() {
return next(1) != 0;
}
/**
* Returns the next pseudorandom, uniformly distributed {@code float}
* value between {@code 0.0} and {@code 1.0} from this random
* number generator's sequence.
*
* The general contract of {@code nextFloat} is that one * {@code float} value, chosen (approximately) uniformly from the * range {@code 0.0f} (inclusive) to {@code 1.0f} (exclusive), is * pseudorandomly generated and returned. All 224 possible * {@code float} values of the form m x 2-24, * where m is a positive integer less than 224, are * produced with (approximately) equal probability. * *
The method {@code nextFloat} is implemented by class {@code Random} * as if by: *
{@code
* 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 {@code float} * values from the stated range with perfect uniformity.
* [In early versions of Java, the result was incorrectly calculated as: *
{@code
* 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.]
*
* @return the next pseudorandom, uniformly distributed {@code float}
* value between {@code 0.0} and {@code 1.0} from this
* random number generator's sequence
*/
public float nextFloat() {
return next(24) / ((float)(1 << 24));
}
/**
* Returns the next pseudorandom, uniformly distributed
* {@code double} value between {@code 0.0} and
* {@code 1.0} from this random number generator's sequence.
*
* The general contract of {@code nextDouble} is that one * {@code double} value, chosen (approximately) uniformly from the * range {@code 0.0d} (inclusive) to {@code 1.0d} (exclusive), is * pseudorandomly generated and returned. * *
The method {@code nextDouble} is implemented by class {@code Random} * as if by: *
{@code
* 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 {@code 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 * {@code double} values from the stated range with perfect uniformity. *
[In early versions of Java, the result was incorrectly calculated as: *
{@code
* 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.]
*
* @return the next pseudorandom, uniformly distributed {@code double}
* value between {@code 0.0} and {@code 1.0} from this
* random number generator's sequence
* @see Math#random
*/
public double nextDouble() {
return (((long)(next(26)) << 27) + next(27)) * DOUBLE_UNIT;
}
private double nextNextGaussian;
private boolean haveNextNextGaussian = false;
/**
* Returns the next pseudorandom, Gaussian ("normally") distributed
* {@code double} value with mean {@code 0.0} and standard
* deviation {@code 1.0} from this random number generator's sequence.
* * The general contract of {@code nextGaussian} is that one * {@code double} value, chosen from (approximately) the usual * normal distribution with mean {@code 0.0} and standard deviation * {@code 1.0}, is pseudorandomly generated and returned. * *
The method {@code nextGaussian} is implemented by class * {@code Random} as if by a threadsafe version of the following: *
{@code
* 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 3: 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 {@code StrictMath.log}
* and one call to {@code StrictMath.sqrt}.
*
* @return the next pseudorandom, Gaussian ("normally") distributed
* {@code double} value with mean {@code 0.0} and
* standard deviation {@code 1.0} from this random number
* generator's sequence
*/
synchronized public double nextGaussian() {
// See Knuth, ACP, Section 3.4.1 Algorithm C.
if (haveNextNextGaussian) {
haveNextNextGaussian = false;
return nextNextGaussian;
} else {
double v1, v2, s;
do {
v1 = 2 * nextDouble() - 1; // between -1 and 1
v2 = 2 * nextDouble() - 1; // between -1 and 1
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;
}
}
// stream methods, coded in a way intended to better isolate for
// maintenance purposes the small differences across forms.
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code int} values.
*
* A pseudorandom {@code int} value is generated as if it's the result of * calling the method {@link #nextInt()}. * * @param streamSize the number of values to generate * @return a stream of pseudorandom {@code int} values * @throws IllegalArgumentException if {@code streamSize} is * less than zero * @since 1.8 */ public IntStream ints(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.intStream (new RandomIntsSpliterator (this, 0L, streamSize, Integer.MAX_VALUE, 0), false); } /** * Returns an effectively unlimited stream of pseudorandom {@code int} * values. * *
A pseudorandom {@code int} value is generated as if it's the result of * calling the method {@link #nextInt()}. * * @implNote This method is implemented to be equivalent to {@code * ints(Long.MAX_VALUE)}. * * @return a stream of pseudorandom {@code int} values * @since 1.8 */ public IntStream ints() { return StreamSupport.intStream (new RandomIntsSpliterator (this, 0L, Long.MAX_VALUE, Integer.MAX_VALUE, 0), false); } /** * Returns a stream producing the given {@code streamSize} number * of pseudorandom {@code int} values, each conforming to the given * origin (inclusive) and bound (exclusive). * *
A pseudorandom {@code 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;
* }
* }}
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public IntStream ints(long streamSize, int randomNumberOrigin,
int randomNumberBound) {
if (streamSize < 0L)
throw new IllegalArgumentException(BadSize);
if (randomNumberOrigin >= randomNumberBound)
throw new IllegalArgumentException(BadRange);
return StreamSupport.intStream
(new RandomIntsSpliterator
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* int} values, each conforming to the given origin (inclusive) and bound
* (exclusive).
*
* A pseudorandom {@code 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;
* }
* }}
*
* @implNote This method is implemented to be equivalent to {@code
* ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
if (randomNumberOrigin >= randomNumberBound)
throw new IllegalArgumentException(BadRange);
return StreamSupport.intStream
(new RandomIntsSpliterator
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code long} values.
*
* A pseudorandom {@code long} value is generated as if it's the result * of calling the method {@link #nextLong()}. * * @param streamSize the number of values to generate * @return a stream of pseudorandom {@code long} values * @throws IllegalArgumentException if {@code streamSize} is * less than zero * @since 1.8 */ public LongStream longs(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.longStream (new RandomLongsSpliterator (this, 0L, streamSize, Long.MAX_VALUE, 0L), false); } /** * Returns an effectively unlimited stream of pseudorandom {@code long} * values. * *
A pseudorandom {@code long} value is generated as if it's the result * of calling the method {@link #nextLong()}. * * @implNote This method is implemented to be equivalent to {@code * longs(Long.MAX_VALUE)}. * * @return a stream of pseudorandom {@code long} values * @since 1.8 */ public LongStream longs() { return StreamSupport.longStream (new RandomLongsSpliterator (this, 0L, Long.MAX_VALUE, Long.MAX_VALUE, 0L), false); } /** * Returns a stream producing the given {@code streamSize} number of * pseudorandom {@code long}, each conforming to the given origin * (inclusive) and bound (exclusive). * *
A pseudorandom {@code 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;
* }}
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public LongStream longs(long streamSize, long randomNumberOrigin,
long randomNumberBound) {
if (streamSize < 0L)
throw new IllegalArgumentException(BadSize);
if (randomNumberOrigin >= randomNumberBound)
throw new IllegalArgumentException(BadRange);
return StreamSupport.longStream
(new RandomLongsSpliterator
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* long} values, each conforming to the given origin (inclusive) and bound
* (exclusive).
*
* A pseudorandom {@code 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;
* }}
*
* @implNote This method is implemented to be equivalent to {@code
* longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
if (randomNumberOrigin >= randomNumberBound)
throw new IllegalArgumentException(BadRange);
return StreamSupport.longStream
(new RandomLongsSpliterator
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Returns a stream producing the given {@code streamSize} number of
* pseudorandom {@code double} values, each between zero
* (inclusive) and one (exclusive).
*
* A pseudorandom {@code double} value is generated as if it's the result * of calling the method {@link #nextDouble()}. * * @param streamSize the number of values to generate * @return a stream of {@code double} values * @throws IllegalArgumentException if {@code streamSize} is * less than zero * @since 1.8 */ public DoubleStream doubles(long streamSize) { if (streamSize < 0L) throw new IllegalArgumentException(BadSize); return StreamSupport.doubleStream (new RandomDoublesSpliterator (this, 0L, streamSize, Double.MAX_VALUE, 0.0), false); } /** * Returns an effectively unlimited stream of pseudorandom {@code * double} values, each between zero (inclusive) and one * (exclusive). * *
A pseudorandom {@code double} value is generated as if it's the result * of calling the method {@link #nextDouble()}. * * @implNote This method is implemented to be equivalent to {@code * doubles(Long.MAX_VALUE)}. * * @return a stream of pseudorandom {@code double} values * @since 1.8 */ public DoubleStream doubles() { return StreamSupport.doubleStream (new RandomDoublesSpliterator (this, 0L, Long.MAX_VALUE, Double.MAX_VALUE, 0.0), false); } /** * Returns a stream producing the given {@code streamSize} number of * pseudorandom {@code double} values, each conforming to the given origin * (inclusive) and bound (exclusive). * *
A pseudorandom {@code 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;
* }}
*
* @param streamSize the number of values to generate
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public DoubleStream doubles(long streamSize, double randomNumberOrigin,
double randomNumberBound) {
if (streamSize < 0L)
throw new IllegalArgumentException(BadSize);
if (!(randomNumberOrigin < randomNumberBound))
throw new IllegalArgumentException(BadRange);
return StreamSupport.doubleStream
(new RandomDoublesSpliterator
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Returns an effectively unlimited stream of pseudorandom {@code
* double} values, each conforming to the given origin (inclusive) and bound
* (exclusive).
*
* A pseudorandom {@code 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;
* }}
*
* @implNote This method is implemented to be equivalent to {@code
* doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
* @param randomNumberOrigin the origin (inclusive) of each random value
* @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
* each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
* @since 1.8
*/
public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
if (!(randomNumberOrigin < randomNumberBound))
throw new IllegalArgumentException(BadRange);
return StreamSupport.doubleStream
(new RandomDoublesSpliterator
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
false);
}
/**
* Spliterator for int streams. We multiplex the four int
* versions into one class by treating a bound less than origin as
* unbounded, and also by treating "infinite" as equivalent to
* Long.MAX_VALUE. For splits, it uses the standard divide-by-two
* approach. The long and double versions of this class are
* identical except for types.
*/
static final class RandomIntsSpliterator implements Spliterator.OfInt {
final Random rng;
long index;
final long fence;
final int origin;
final int bound;
RandomIntsSpliterator(Random rng, long index, long fence,
int origin, int bound) {
this.rng = rng; this.index = index; this.fence = fence;
this.origin = origin; this.bound = bound;
}
public RandomIntsSpliterator trySplit() {
long i = index, m = (i + fence) >>> 1;
return (m <= i) ? null :
new RandomIntsSpliterator(rng, i, index = m, origin, bound);
}
public long estimateSize() {
return fence - index;
}
public int characteristics() {
return (Spliterator.SIZED | Spliterator.SUBSIZED |
Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
public boolean tryAdvance(IntConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
consumer.accept(rng.internalNextInt(origin, bound));
index = i + 1;
return true;
}
return false;
}
public void forEachRemaining(IntConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
index = f;
Random r = rng;
int o = origin, b = bound;
do {
consumer.accept(r.internalNextInt(o, b));
} while (++i < f);
}
}
}
/**
* Spliterator for long streams.
*/
static final class RandomLongsSpliterator implements Spliterator.OfLong {
final Random rng;
long index;
final long fence;
final long origin;
final long bound;
RandomLongsSpliterator(Random rng, long index, long fence,
long origin, long bound) {
this.rng = rng; this.index = index; this.fence = fence;
this.origin = origin; this.bound = bound;
}
public RandomLongsSpliterator trySplit() {
long i = index, m = (i + fence) >>> 1;
return (m <= i) ? null :
new RandomLongsSpliterator(rng, i, index = m, origin, bound);
}
public long estimateSize() {
return fence - index;
}
public int characteristics() {
return (Spliterator.SIZED | Spliterator.SUBSIZED |
Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
public boolean tryAdvance(LongConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
consumer.accept(rng.internalNextLong(origin, bound));
index = i + 1;
return true;
}
return false;
}
public void forEachRemaining(LongConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
index = f;
Random r = rng;
long o = origin, b = bound;
do {
consumer.accept(r.internalNextLong(o, b));
} while (++i < f);
}
}
}
/**
* Spliterator for double streams.
*/
static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
final Random rng;
long index;
final long fence;
final double origin;
final double bound;
RandomDoublesSpliterator(Random rng, long index, long fence,
double origin, double bound) {
this.rng = rng; this.index = index; this.fence = fence;
this.origin = origin; this.bound = bound;
}
public RandomDoublesSpliterator trySplit() {
long i = index, m = (i + fence) >>> 1;
return (m <= i) ? null :
new RandomDoublesSpliterator(rng, i, index = m, origin, bound);
}
public long estimateSize() {
return fence - index;
}
public int characteristics() {
return (Spliterator.SIZED | Spliterator.SUBSIZED |
Spliterator.NONNULL | Spliterator.IMMUTABLE);
}
public boolean tryAdvance(DoubleConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
consumer.accept(rng.internalNextDouble(origin, bound));
index = i + 1;
return true;
}
return false;
}
public void forEachRemaining(DoubleConsumer consumer) {
if (consumer == null) throw new NullPointerException();
long i = index, f = fence;
if (i < f) {
index = f;
Random r = rng;
double o = origin, b = bound;
do {
consumer.accept(r.internalNextDouble(o, b));
} while (++i < f);
}
}
}
/**
* Serializable fields for Random.
*
* @serialField seed long
* seed for random computations
* @serialField nextNextGaussian double
* next Gaussian to be returned
* @serialField haveNextNextGaussian boolean
* nextNextGaussian is valid
*/
private static final ObjectStreamField[] serialPersistentFields = {
new ObjectStreamField("seed", Long.TYPE),
new ObjectStreamField("nextNextGaussian", Double.TYPE),
new ObjectStreamField("haveNextNextGaussian", Boolean.TYPE)
};
/**
* Reconstitute the {@code Random} instance from a stream (that is,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
ObjectInputStream.GetField fields = s.readFields();
// The seed is read in as {@code long} for
// historical reasons, but it is converted to an AtomicLong.
long seedVal = fields.get("seed", -1L);
if (seedVal < 0)
throw new java.io.StreamCorruptedException(
"Random: invalid seed");
resetSeed(seedVal);
nextNextGaussian = fields.get("nextNextGaussian", 0.0);
haveNextNextGaussian = fields.get("haveNextNextGaussian", false);
}
/**
* Save the {@code Random} instance to a stream.
*/
synchronized private void writeObject(ObjectOutputStream s)
throws IOException {
// set the values of the Serializable fields
ObjectOutputStream.PutField fields = s.putFields();
// The seed is serialized as a long for historical reasons.
fields.put("seed", seed.get());
fields.put("nextNextGaussian", nextNextGaussian);
fields.put("haveNextNextGaussian", haveNextNextGaussian);
// save them
s.writeFields();
}
// Support for resetting seed while deserializing
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long seedOffset;
static {
try {
seedOffset = unsafe.objectFieldOffset
(Random.class.getDeclaredField("seed"));
} catch (Exception ex) { throw new Error(ex); }
}
private void resetSeed(long seedVal) {
unsafe.putObjectVolatile(this, seedOffset, new AtomicLong(seedVal));
}
}