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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 singlelong seed. The seed is the initial value of the internal state of the pseudorandom number generator which is maintained by methodnext(int).

  Implementation Requirements:

  The invocationnew Random(seed) is equivalent to:

   Random rnd = new Random(); rnd.setSeed(seed);

  Parameters:

  seed - the initial seed

  See Also:

  • setSeed(long)

Method Details

• from

  public static Random from(RandomGenerator generator)

  Returns an instance ofRandom that delegates method calls to theRandomGenerator argument. If the generator is an instance ofRandom, it is returned. Otherwise, this method returns an instance ofRandom that delegates all methods exceptsetSeed to the generator. The returned instance'ssetSeed method always throwsUnsupportedOperationException. The returned instance is not serializable.

  Parameters:

  generator - theRandomGenerator calls are delegated to

  Returns:

  the delegatingRandom 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 providedlong seed value (optional operation).

  Implementation Requirements:

  The implementation in this class alters the state of this random number generator so that it is in the same state as if it had just been created withnew Random(seed). It atomically updates the seed to

  (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)

  and clears thehaveNextNextGaussian flag used bynextGaussian(). Note that this uses only 48 bits of the given seed value.

  Parameters:

  seed - the seed value

  Throws:

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

• next

  protected int next(int bits)

  Generates the next pseudorandom number. This method returns anint value such that, if the argumentbits is between1 and32 (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 be0 or1.

  API Note:

  The other random-producing methods in this class are implemented in terms of this method, so subclasses can override just this method to provide a different source of pseudorandom numbers for the entire class.

  Implementation Requirements:

  The implementation in this class atomically updates the seed to

  (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 inThe Art of Computer Programming, Volume 2, Third edition: Seminumerical Algorithms, section 3.2.1.

  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

  Implementation Requirements:

  The methodnextBytes is implemented by classRandom 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; }

  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 distributedint value from this random number generator's sequence. The general contract ofnextInt is that oneint value is pseudorandomly generated and returned. All 2³² possibleint values are produced with (approximately) equal probability.

  Specified by:

  nextInt in interface RandomGenerator

  Implementation Requirements:

  The methodnextInt is implemented by classRandom as if by:

   public int nextInt() {   return next(32); }

  Returns:

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

• nextInt

  public int nextInt(int bound)

  Returns a pseudorandom, uniformly distributedint value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract ofnextInt is that oneint value in the specified range is pseudorandomly generated and returned. Allbound possibleint values are produced with (approximately) equal probability.

  Specified by:

  nextInt in interface RandomGenerator

  Implementation Requirements:

  The methodnextInt(int bound) is implemented by classRandom 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 chooseint 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 oflow-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.

  Parameters:

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

  Returns:

  the next pseudorandom, uniformly distributedint value between zero (inclusive) andbound (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 distributedlong value from this random number generator's sequence. The general contract ofnextLong is that onelong value is pseudorandomly generated and returned.

  Specified by:

  nextLong in interface RandomGenerator

  Implementation Requirements:

  The methodnextLong is implemented by classRandom as if by:

   public long nextLong() {   return ((long)next(32) << 32) + next(32); }

  Because classRandom uses a seed with only 48 bits, this algorithm will not return all possiblelong values.

  Returns:

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

• nextBoolean

  public boolean nextBoolean()

  Returns the next pseudorandom, uniformly distributedboolean value from this random number generator's sequence. The general contract ofnextBoolean is that oneboolean value is pseudorandomly generated and returned. The valuestrue andfalse are produced with (approximately) equal probability.

  Specified by:

  nextBoolean in interface RandomGenerator

  Implementation Requirements:

  The methodnextBoolean is implemented by classRandom as if by:

   public boolean nextBoolean() {   return next(1) != 0; }

  Returns:

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

  Since:

  1.2

• nextFloat

  public float nextFloat()

  Returns the next pseudorandom, uniformly distributedfloat value between0.0 and1.0 from this random number generator's sequence.

  The general contract ofnextFloat is that onefloat value, chosen (approximately) uniformly from the range0.0f (inclusive) to1.0f (exclusive), is pseudorandomly generated and returned. All 2²⁴ possiblefloat values of the formm x 2^-24, wherem is a positive integer less than 2²⁴, are produced with (approximately) equal probability.

  Specified by:

  nextFloat in interface RandomGenerator

  Implementation Requirements:

  The methodnextFloat is implemented by classRandom 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 choosefloat 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.]

  Returns:

  the next pseudorandom, uniformly distributedfloat value between0.0f and1.0f from this random number generator's sequence

• nextDouble

  public double nextDouble()

  Returns the next pseudorandom, uniformly distributeddouble value between0.0 and1.0 from this random number generator's sequence.

  The general contract ofnextDouble is that onedouble value, chosen (approximately) uniformly from the range0.0d (inclusive) to1.0d (exclusive), is pseudorandomly generated and returned.

  Specified by:

  nextDouble in interface RandomGenerator

  Implementation Requirements:

  The methodnextDouble is implemented by classRandom 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 thenext 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 choosedouble 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.]

  Returns:

  the next pseudorandom, uniformly distributeddouble value between0.0 and1.0 from this random number generator's sequence

  See Also:

  • Math.random()

• nextGaussian

  public double nextGaussian()

  Returns the next pseudorandom, Gaussian ("normally") distributeddouble value with mean0.0 and standard deviation1.0 from this random number generator's sequence.

  The general contract ofnextGaussian is that onedouble value, chosen from (approximately) the usual normal distribution with mean0.0 and standard deviation1.0, is pseudorandomly generated and returned.

  Specified by:

  nextGaussian in interface RandomGenerator

  Implementation Requirements:

  The methodnextGaussian is implemented by classRandom 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 thepolar method of G. E. P. Box, M. E. Muller, and G. Marsaglia, as described by Donald E. Knuth inThe 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 toStrictMath.log and one call toStrictMath.sqrt.

  Returns:

  the next pseudorandom, Gaussian ("normally") distributeddouble value with mean0.0 and standard deviation1.0 from this random number generator's sequence

• ints

  public IntStream ints(long streamSize)

  Returns a stream producing the givenstreamSize number of pseudorandomint values.

  A pseudorandomint value is generated as if it's the result of calling the methodnextInt().

  Specified by:

  ints in interface RandomGenerator

  Parameters:

  streamSize - the number of values to generate

  Returns:

  a stream of pseudorandomint values

  Throws:

  IllegalArgumentException - ifstreamSize is less than zero

  Since:

  1.8

• ints

  public IntStream ints()

  Returns an effectively unlimited stream of pseudorandomint values.

  A pseudorandomint value is generated as if it's the result of calling the methodnextInt().

  Specified by:

  ints in interface RandomGenerator

  Implementation Note:

  This method is implemented to be equivalent to ints(Long.MAX_VALUE).

  Returns:

  a stream of pseudorandomint values

  Since:

  1.8

• ints

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

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

  A pseudorandomint 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 pseudorandomint values, each with the given origin (inclusive) and bound (exclusive)

  Throws:

  IllegalArgumentException - ifstreamSize is less than zero, orrandomNumberOrigin is greater than or equal torandomNumberBound

  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 pseudorandomint 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

  Implementation Note:

  This method is implemented to be equivalent to ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

  Parameters:

  randomNumberOrigin - the origin (inclusive) of each random value

  randomNumberBound - the bound (exclusive) of each random value

  Returns:

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

  Throws:

  IllegalArgumentException - ifrandomNumberOrigin is greater than or equal torandomNumberBound

  Since:

  1.8

• longs

  public LongStream longs(long streamSize)

  Returns a stream producing the givenstreamSize number of pseudorandomlong values.

  A pseudorandomlong value is generated as if it's the result of calling the methodnextLong().

  Specified by:

  longs in interface RandomGenerator

  Parameters:

  streamSize - the number of values to generate

  Returns:

  a stream of pseudorandomlong values

  Throws:

  IllegalArgumentException - ifstreamSize is less than zero

  Since:

  1.8

• longs

  public LongStream longs()

  Returns an effectively unlimited stream of pseudorandomlong values.

  A pseudorandomlong value is generated as if it's the result of calling the methodnextLong().

  Specified by:

  longs in interface RandomGenerator

  Implementation Note:

  This method is implemented to be equivalent to longs(Long.MAX_VALUE).

  Returns:

  a stream of pseudorandomlong values

  Since:

  1.8

• longs

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

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

  A pseudorandomlong 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 pseudorandomlong values, each with the given origin (inclusive) and bound (exclusive)

  Throws:

  IllegalArgumentException - ifstreamSize is less than zero, orrandomNumberOrigin is greater than or equal torandomNumberBound

  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 pseudorandomlong 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

  Implementation Note:

  This method is implemented to be equivalent to longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

  Parameters:

  randomNumberOrigin - the origin (inclusive) of each random value

  randomNumberBound - the bound (exclusive) of each random value

  Returns:

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

  Throws:

  IllegalArgumentException - ifrandomNumberOrigin is greater than or equal torandomNumberBound

  Since:

  1.8

• doubles

  public DoubleStream doubles(long streamSize)

  Returns a stream producing the givenstreamSize number of pseudorandomdouble values, each between zero (inclusive) and one (exclusive).

  A pseudorandomdouble value is generated as if it's the result of calling the methodnextDouble().

  Specified by:

  doubles in interface RandomGenerator

  Parameters:

  streamSize - the number of values to generate

  Returns:

  a stream ofdouble values

  Throws:

  IllegalArgumentException - ifstreamSize 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 pseudorandomdouble value is generated as if it's the result of calling the methodnextDouble().

  Specified by:

  doubles in interface RandomGenerator

  Implementation Note:

  This method is implemented to be equivalent to doubles(Long.MAX_VALUE).

  Returns:

  a stream of pseudorandomdouble values

  Since:

  1.8

• doubles

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

  Returns a stream producing the givenstreamSize number of pseudorandomdouble 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 pseudorandomdouble values, each with the given origin (inclusive) and bound (exclusive)

  Throws:

  IllegalArgumentException - ifstreamSize is less than zero, orrandomNumberOrigin is not finite, orrandomNumberBound is not finite, orrandomNumberOrigin is greater than or equal torandomNumberBound

  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

  Implementation Note:

  This method is implemented to be equivalent to doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).

  Parameters:

  randomNumberOrigin - the origin (inclusive) of each random value

  randomNumberBound - the bound (exclusive) of each random value

  Returns:

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

  Throws:

  IllegalArgumentException - ifrandomNumberOrigin is not finite, orrandomNumberBound is not finite, orrandomNumberOrigin is greater than or equal torandomNumberBound

  Since:

  1.8