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Class ThreadLocalRandom

java.lang.Object

java.util.Random

java.util.concurrent.ThreadLocalRandom

All Implemented Interfaces:: Serializable, RandomGenerator

public final class ThreadLocalRandom extends Random

A random number generator (with period 2⁶⁴) isolated to the current thread. Like the global Random generator used by the Math class, a ThreadLocalRandom is initialized with an internally generated seed that may not otherwise be modified. When applicable, use of ThreadLocalRandom rather than shared Random objects in concurrent programs will typically encounter much less overhead and contention. Use of ThreadLocalRandom is particularly appropriate when multiple tasks (for example, each a ForkJoinTask) use random numbers in parallel in thread pools.

Usages of this class should typically be of the form: ThreadLocalRandom.current().nextX(...) (where X is Int, Long, etc). When all usages are of this form, it is never possible to accidentally share a ThreadLocalRandom across multiple threads.

This class also provides additional commonly used bounded random generation methods.

Instances of ThreadLocalRandom are not cryptographically secure. Consider instead using SecureRandom in security-sensitive applications. Additionally, default-constructed instances do not use a cryptographically random seed unless the system property java.util.secureRandomSeed is set to true.

Since:

1.7

See Also:

Nested Class Summary

Nested classes/interfaces declared in interface java.util.random.RandomGenerator

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

Method Summary

Modifier and Type	Method	Description
`static ThreadLocalRandom`	`current()`	Returns the current thread's `ThreadLocalRandom` object.
`DoubleStream`	`doubles()`	Returns an effectively unlimited stream of pseudorandom `double` values, each between zero (inclusive) and one (exclusive).
`DoubleStream`	`doubles(double randomNumberOrigin, double randomNumberBound)`	Returns an effectively unlimited stream of pseudorandom `double` values, each conforming to the given origin (inclusive) and bound (exclusive).
`DoubleStream`	`doubles(long streamSize)`	Returns a stream producing the given `streamSize` number of pseudorandom `double` values, each between zero (inclusive) and one (exclusive).
`DoubleStream`	`doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)`	Returns a stream producing the given `streamSize` number of pseudorandom `double` values, each conforming to the given origin (inclusive) and bound (exclusive).
`IntStream`	`ints()`	Returns an effectively unlimited stream of pseudorandom `int` values.
`IntStream`	`ints(int randomNumberOrigin, int randomNumberBound)`	Returns an effectively unlimited stream of pseudorandom `int` values, each conforming to the given origin (inclusive) and bound (exclusive).
`IntStream`	`ints(long streamSize)`	Returns a stream producing the given `streamSize` number of pseudorandom `int` values.
`IntStream`	`ints(long streamSize, int randomNumberOrigin, int randomNumberBound)`	Returns a stream producing the given `streamSize` number of pseudorandom `int` values, each conforming to the given origin (inclusive) and bound (exclusive).
`LongStream`	`longs()`	Returns an effectively unlimited stream of pseudorandom `long` values.
`LongStream`	`longs(long streamSize)`	Returns a stream producing the given `streamSize` number of pseudorandom `long` values.
`LongStream`	`longs(long randomNumberOrigin, long randomNumberBound)`	Returns an effectively unlimited stream of pseudorandom `long` values, each conforming to the given origin (inclusive) and bound (exclusive).
`LongStream`	`longs(long streamSize, long randomNumberOrigin, long randomNumberBound)`	Returns a stream producing the given `streamSize` number of pseudorandom `long`, each conforming to the given origin (inclusive) and bound (exclusive).
`protected int`	`next(int bits)`	Generates a pseudorandom number with the indicated number of low-order bits.
`double`	`nextDouble(double bound)`	Returns a pseudorandomly chosen `double` value between zero (inclusive) and the specified bound (exclusive).
`double`	`nextDouble(double origin, double bound)`	Returns a pseudorandomly chosen `double` value between the specified origin (inclusive) and the specified bound (exclusive).
`float`	`nextFloat(float bound)`	Returns a pseudorandomly chosen `float` value between zero (inclusive) and the specified bound (exclusive).
`float`	`nextFloat(float origin, float bound)`	Returns a pseudorandomly chosen `float` value between the specified origin (inclusive) and the specified bound (exclusive).
`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.
`int`	`nextInt(int origin, int bound)`	Returns a pseudorandomly chosen `int` value between the specified origin (inclusive) and the specified bound (exclusive).
`long`	`nextLong(long bound)`	Returns a pseudorandomly chosen `long` value between zero (inclusive) and the specified bound (exclusive).
`long`	`nextLong(long origin, long bound)`	Returns a pseudorandomly chosen `long` value between the specified origin (inclusive) and the specified bound (exclusive).
`void`	`setSeed(long seed)`	Throws `UnsupportedOperationException`.

Methods declared in class java.util.Random

from, nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextLong

Methods declared in class java.lang.Object

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

Methods declared in interface java.util.random.RandomGenerator

isDeprecated, nextExponential, nextGaussian

Method Details

current

public static ThreadLocalRandom current()

Returns the current thread's ThreadLocalRandom object. Methods of this object should be called only by the current thread, not by other threads.

Returns:: the current thread's ThreadLocalRandom

setSeed

public void setSeed(long seed)

Throws UnsupportedOperationException. Setting seeds in this generator is not supported.

Overrides:: setSeed in class Random
Parameters:: seed - the seed value
Throws:: UnsupportedOperationException - always

protected int next(int bits)

Generates a pseudorandom number with the indicated number of low-order bits. Because this class has no subclasses, this method cannot be invoked or overridden.

Overrides:: next in class Random
Parameters:: bits - random bits
Returns:: the next pseudorandom value from this random number generator's sequence

nextInt

public int nextInt(int bound)

Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.

Specified by:: nextInt in interface RandomGenerator
Overrides:: nextInt in class Random
Parameters:: bound - the upper bound (exclusive). Must be positive.
Returns:: the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence
Throws:: IllegalArgumentException - if bound is not positive

nextInt

public int nextInt(int origin, int bound)

Returns a pseudorandomly chosen int value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:: origin - the least value that can be returned; bound - the upper bound (exclusive) for the returned value
Returns:: a pseudorandomly chosen int value between the origin (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if origin is greater than or equal to bound

nextLong

public long nextLong(long bound)

Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).

Parameters:: bound - the upper bound (exclusive) for the returned value. Must be positive.
Returns:: a pseudorandomly chosen long value between zero (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if bound is not positive

nextLong

public long nextLong(long origin, long bound)

Returns a pseudorandomly chosen long value between the specified origin (inclusive) and the specified bound (exclusive).

Parameters:: origin - the least value that can be returned; bound - the upper bound (exclusive) for the returned value
Returns:: a pseudorandomly chosen long value between the origin (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if origin is greater than or equal to bound

nextFloat

public float nextFloat(float bound)

Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).

Implementation Note:
Parameters:: bound - the upper bound (exclusive) for the returned value. Must be positive and finite
Returns:: a pseudorandomly chosen float value between zero (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if bound is not both positive and finite

nextFloat

public float nextFloat(float origin, float bound)

Returns a pseudorandomly chosen float value between the specified origin (inclusive) and the specified bound (exclusive).

Implementation Note:
Parameters:: origin - the least value that can be returned; bound - the upper bound (exclusive)
Returns:: a pseudorandomly chosen float value between the origin (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

nextDouble

public double nextDouble(double bound)

Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).

Implementation Note:
Parameters:: bound - the upper bound (exclusive) for the returned value. Must be positive and finite
Returns:: a pseudorandomly chosen double value between zero (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if bound is not both positive and finite

nextDouble

public double nextDouble(double origin, double bound)

Returns a pseudorandomly chosen double value between the specified origin (inclusive) and the specified bound (exclusive).

Implementation Note:
Parameters:: origin - the least value that can be returned; bound - the upper bound (exclusive) for the returned value
Returns:: a pseudorandomly chosen double value between the origin (inclusive) and the bound (exclusive)
Throws:: IllegalArgumentException - if origin is not finite, or bound is not finite, or origin is greater than or equal to bound

ints

public IntStream ints(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

Specified by:: ints in interface RandomGenerator
Overrides:: ints in class Random
Parameters:: streamSize - the number of values to generate
Returns:: a stream of pseudorandom int values
Throws:: IllegalArgumentException - if streamSize is less than zero
Since:: 1.8

ints

public IntStream ints()

Returns an effectively unlimited stream of pseudorandom int values.

A pseudorandom int value is generated as if it's the result of calling the method Random.nextInt().

Specified by:: ints in interface RandomGenerator
Overrides:: ints in class Random
Implementation Note:: This method is implemented to be equivalent to ints(Long.MAX_VALUE).
Returns:: a stream of pseudorandom int values
Since:: 1.8

ints

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

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

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

 
 int nextInt(int origin, int bound) {
   int n = bound - origin;
   if (n > 0) {
     return nextInt(n) + origin;
   }
   else {  // range not representable as int
     int r;
     do {
       r = nextInt();
     } while (r < origin || r >= bound);
     return r;
   }
 }

Specified by:: ints in interface RandomGenerator
Overrides:: ints in class Random
Parameters:: streamSize - the number of values to generate; randomNumberOrigin - the origin (inclusive) of each random value; randomNumberBound - the bound (exclusive) of each random value
Returns:: a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

ints

public IntStream ints(int randomNumberOrigin, int randomNumberBound)

Returns an effectively unlimited stream of pseudorandom

int

values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom int value is generated as if it's the result of calling the following method with the origin and bound:

 
 int nextInt(int origin, int bound) {
   int n = bound - origin;
   if (n > 0) {
     return nextInt(n) + origin;
   }
   else {  // range not representable as int
     int r;
     do {
       r = nextInt();
     } while (r < origin || r >= bound);
     return r;
   }
 }

Specified by:: ints in interface RandomGenerator
Overrides:: ints in class Random
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 pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

longs

public LongStream longs(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

Specified by:: longs in interface RandomGenerator
Overrides:: longs in class Random
Parameters:: streamSize - the number of values to generate
Returns:: a stream of pseudorandom long values
Throws:: IllegalArgumentException - if streamSize is less than zero
Since:: 1.8

longs

public LongStream longs()

Returns an effectively unlimited stream of pseudorandom long values.

A pseudorandom long value is generated as if it's the result of calling the method Random.nextLong().

Specified by:: longs in interface RandomGenerator
Overrides:: longs in class Random
Implementation Note:: This method is implemented to be equivalent to longs(Long.MAX_VALUE).
Returns:: a stream of pseudorandom long values
Since:: 1.8

longs

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

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

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

 
 long nextLong(long origin, long bound) {
   long r = nextLong();
   long n = bound - origin, m = n - 1;
   if ((n & m) == 0L)  // power of two
     r = (r & m) + origin;
   else if (n > 0L) {  // reject over-represented candidates
     for (long u = r >>> 1;            // ensure nonnegative
          u + m - (r = u % n) < 0L;    // rejection check
          u = nextLong() >>> 1) // retry
         ;
     r += origin;
   }
   else {              // range not representable as long
     while (r < origin || r >= bound)
       r = nextLong();
   }
   return r;
 }

Specified by:: longs in interface RandomGenerator
Overrides:: longs in class Random
Parameters:: streamSize - the number of values to generate; randomNumberOrigin - the origin (inclusive) of each random value; randomNumberBound - the bound (exclusive) of each random value
Returns:: a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if streamSize is less than zero, or randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

longs

public LongStream longs(long randomNumberOrigin, long randomNumberBound)

Returns an effectively unlimited stream of pseudorandom


 long

values, each conforming to the given origin (inclusive) and bound (exclusive).

A pseudorandom long value is generated as if it's the result of calling the following method with the origin and bound:

 
 long nextLong(long origin, long bound) {
   long r = nextLong();
   long n = bound - origin, m = n - 1;
   if ((n & m) == 0L)  // power of two
     r = (r & m) + origin;
   else if (n > 0L) {  // reject over-represented candidates
     for (long u = r >>> 1;            // ensure nonnegative
          u + m - (r = u % n) < 0L;    // rejection check
          u = nextLong() >>> 1) // retry
         ;
     r += origin;
   }
   else {              // range not representable as long
     while (r < origin || r >= bound)
       r = nextLong();
   }
   return r;
 }

Specified by:: longs in interface RandomGenerator
Overrides:: longs in class Random
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 pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

doubles

public DoubleStream doubles(long streamSize)

Returns a stream producing the given streamSize number of pseudorandom double values, each between zero (inclusive) and one (exclusive).

A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

Specified by:: doubles in interface RandomGenerator
Overrides:: doubles in class Random
Parameters:: streamSize - the number of values to generate
Returns:: a stream of double values
Throws:: IllegalArgumentException - if streamSize is less than zero
Since:: 1.8

doubles

public DoubleStream doubles()

Returns an effectively unlimited stream of pseudorandom


 double

values, each between zero (inclusive) and one (exclusive).

A pseudorandom double value is generated as if it's the result of calling the method Random.nextDouble().

Specified by:: doubles in interface RandomGenerator
Overrides:: doubles in class Random
Implementation Note:: This method is implemented to be equivalent to doubles(Long.MAX_VALUE).
Returns:: a stream of pseudorandom double values
Since:: 1.8

doubles

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

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

Specified by:: doubles in interface RandomGenerator
Overrides:: doubles in class Random
Parameters:: streamSize - the number of values to generate; randomNumberOrigin - the origin (inclusive) of each random value; randomNumberBound - the bound (exclusive) of each random value
Returns:: a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if streamSize is less than zero, or randomNumberOrigin is not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

doubles

public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound)

Returns an effectively unlimited stream of pseudorandom


 double

values, each conforming to the given origin (inclusive) and bound (exclusive).

Specified by:: doubles in interface RandomGenerator
Overrides:: doubles in class Random
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 pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)
Throws:: IllegalArgumentException - if randomNumberOrigin is not finite, or randomNumberBound is not finite, or randomNumberOrigin is greater than or equal to randomNumberBound
Since:: 1.8

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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/ThreadLocalRandom.html