Serializable, RandomGenerator
SecureRandom, ThreadLocalRandom
public class Random extends Object implements RandomGenerator, Serializable
 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.
RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator
| Constructor | Description | 
|---|---|
| Random() | Creates a new random number generator. | 
| Random | Creates a new random number generator using a single  longseed. | 
| Modifier and Type | Method | Description | 
|---|---|---|
| DoubleStream | doubles() | Returns an effectively unlimited stream of pseudorandom  
 doublevalues, each between zero (inclusive) and one (exclusive). | 
| DoubleStream | doubles | Returns an effectively unlimited stream of pseudorandom  
 doublevalues, each conforming to the given origin (inclusive) and bound (exclusive). | 
| DoubleStream | doubles | Returns a stream producing the given  streamSizenumber of pseudorandomdoublevalues, each between zero (inclusive) and one (exclusive). | 
| DoubleStream | doubles | Returns a stream producing the given  streamSizenumber of pseudorandomdoublevalues, each conforming to the given origin (inclusive) and bound (exclusive). | 
| static Random | from | Returns an instance of  Randomthat delegates method calls to theRandomGeneratorargument. | 
| IntStream | ints() | Returns an effectively unlimited stream of pseudorandom  intvalues. | 
| IntStream | ints | Returns an effectively unlimited stream of pseudorandom  
 intvalues, each conforming to the given origin (inclusive) and bound (exclusive). | 
| IntStream | ints | Returns a stream producing the given  streamSizenumber of pseudorandomintvalues. | 
| IntStream | ints | Returns a stream producing the given  streamSizenumber of pseudorandomintvalues, each conforming to the given origin (inclusive) and bound (exclusive). | 
| LongStream | longs() | Returns an effectively unlimited stream of pseudorandom  longvalues. | 
| LongStream | longs | Returns a stream producing the given  streamSizenumber of pseudorandomlongvalues. | 
| LongStream | longs | Returns an effectively unlimited stream of pseudorandom  
 longvalues, each conforming to the given origin (inclusive) and bound (exclusive). | 
| LongStream | longs | Returns a stream producing the given  streamSizenumber of pseudorandomlong, each conforming to the given origin (inclusive) and bound (exclusive). | 
| protected int | next | Generates the next pseudorandom number. | 
| boolean | nextBoolean() | Returns the next pseudorandom, uniformly distributed  booleanvalue from this random number generator's sequence. | 
| void | nextBytes | Generates random bytes and places them into a user-supplied byte array. | 
| double | nextDouble() | Returns the next pseudorandom, uniformly distributed  doublevalue between0.0and1.0from this random number generator's sequence. | 
| float | nextFloat() | Returns the next pseudorandom, uniformly distributed  floatvalue between0.0and1.0from this random number generator's sequence. | 
| double | nextGaussian() | Returns the next pseudorandom, Gaussian ("normally") distributed  doublevalue with mean0.0and standard deviation1.0from this random number generator's sequence. | 
| int | nextInt() | Returns the next pseudorandom, uniformly distributed  intvalue from this random number generator's sequence. | 
| int | nextInt | Returns a pseudorandom, uniformly distributed  intvalue between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. | 
| long | nextLong() | Returns the next pseudorandom, uniformly distributed  longvalue from this random number generator's sequence. | 
| void | setSeed | Sets or updates the seed of this random number generator using the provided  longseed value (optional operation). | 
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
isDeprecated, nextDouble, nextDouble, nextExponential, nextFloat, nextFloat, nextGaussian, nextInt, nextLong, nextLong
public Random()
public Random(long seed)
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 seedpublic static Random from(RandomGenerator generator)
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 toRandom instanceNullPointerException - if generator is nullpublic void setSeed(long seed)
long seed value (optional operation).new Random(seed). It atomically updates the seed to (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1)haveNextNextGaussian flag used by nextGaussian(). Note that this uses only 48 bits of the given seed value.seed - the seed valueUnsupportedOperationException - if the setSeed operation is not supported by this random number generatorprotected int next(int bits)
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)(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 bitspublic void nextBytes(byte[] bytes)
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 bytesNullPointerException - if the byte array is nullpublic int nextInt()
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 sequencepublic int nextInt(int bound)
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 sequenceIllegalArgumentException - if bound is not positivepublic long nextLong()
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);
 }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 sequencepublic boolean nextBoolean()
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 sequencepublic float nextFloat()
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 sequencepublic double nextDouble()
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 sequencepublic double nextGaussian()
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;
   }
 }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 sequencepublic IntStream ints(long streamSize)
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 generateint valuesIllegalArgumentException - if streamSize is less than zeropublic IntStream ints()
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 valuespublic IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound)
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 generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valueint 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
public IntStream ints(int randomNumberOrigin, int randomNumberBound)
 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 valuerandomNumberBound - the bound (exclusive) of each random valueint values, each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound
public LongStream longs(long streamSize)
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 generatelong valuesIllegalArgumentException - if streamSize is less than zeropublic LongStream longs()
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 valuespublic LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound)
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 generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuelong 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
public LongStream longs(long randomNumberOrigin, long randomNumberBound)
 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 valuerandomNumberBound - the bound (exclusive) of each random valuelong values, each with the given origin (inclusive) and bound (exclusive)IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound
public DoubleStream doubles(long streamSize)
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 generatedouble valuesIllegalArgumentException - if streamSize is less than zeropublic DoubleStream doubles()
 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 valuespublic DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)
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 generaterandomNumberOrigin - the origin (inclusive) of each random valuerandomNumberBound - the bound (exclusive) of each random valuedouble 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
public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)
 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 valuerandomNumberBound - the bound (exclusive) of each random valuedouble 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
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