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java.base / java.util.concurrent
Class ThreadLocalRandom
java.lang.Object
  java.util.Random
      java.util.concurrent.ThreadLocalRandom
All Implemented Interfaces:
Serializable, RandomGenerator

public 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
Author:
Doug Lea
See Also:
Serialized Form

Nested Class Summary
Nested classes/interfaces inherited from interface java.util.random.RandomGenerator
RandomGenerator.ArbitrarilyJumpableGenerator, RandomGenerator.JumpableGenerator, RandomGenerator.LeapableGenerator, RandomGenerator.SplittableGenerator, RandomGenerator.StreamableGenerator
Method Summary
Returns the current thread's ThreadLocalRandom object.
Returns an effectively unlimited stream of pseudorandom double values, each between zero (inclusive) and one (exclusive).
doubles(double randomNumberOrigin, double randomNumberBound)
Returns an effectively unlimited stream of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).
doubles(long streamSize)
Returns a stream producing the given streamSize number of pseudorandom double values, each between zero (inclusive) and one (exclusive).
doubles(long streamSize, double randomNumberOrigin, double randomNumberBound)
Returns a stream producing the given streamSize number of pseudorandom double values, each conforming to the given origin (inclusive) and bound (exclusive).
Returns an effectively unlimited stream of pseudorandom int values.
ints(int randomNumberOrigin, int randomNumberBound)
Returns an effectively unlimited stream of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).
ints(long streamSize)
Returns a stream producing the given streamSize number of pseudorandom int values.
ints(long streamSize, int randomNumberOrigin, int randomNumberBound)
Returns a stream producing the given streamSize number of pseudorandom int values, each conforming to the given origin (inclusive) and bound (exclusive).
Returns an effectively unlimited stream of pseudorandom long values.
longs(long streamSize)
Returns a stream producing the given streamSize number of pseudorandom long values.
longs(long randomNumberOrigin, long randomNumberBound)
Returns an effectively unlimited stream of pseudorandom long values, each conforming to the given origin (inclusive) and bound (exclusive).
longs(long streamSize, long randomNumberOrigin, long randomNumberBound)
Returns a stream producing the given streamSize number of pseudorandom long, each conforming to the given origin (inclusive) and bound (exclusive).
protected int
next(int bits)
Generates a pseudorandom number with the indicated number of low-order bits.
boolean
Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence.
double
Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.
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
Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.
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
Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence.
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
Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.
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 inherited from class java.util.Random
nextBytes, nextGaussian
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface java.util.random.RandomGenerator
getDefault, isDeprecated, nextExponential, nextGaussian, of
Method Detail
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 initial seed
Throws:
UnsupportedOperationException - always

next
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

nextBoolean
public boolean nextBoolean
()
Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence. The general contract of nextBoolean is that one boolean value is pseudorandomly generated and returned. The values true and false are produced with (approximately) equal probability.
Specified by:
nextBoolean in interface RandomGenerator
Overrides:
nextBoolean in class Random
Returns:
the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence

nextInt
public int nextInt
()
Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence. The general contract of nextInt is that one int value is pseudorandomly generated and returned. All 232 possible int values are produced with (approximately) equal probability.
Specified by:
nextInt in interface RandomGenerator
Overrides:
nextInt in class Random
Returns:
the next pseudorandom, uniformly distributed int 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).
Specified by:
nextInt in interface RandomGenerator
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
()
Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence. The general contract of nextLong is that one long value is pseudorandomly generated and returned.
Specified by:
nextLong in interface RandomGenerator
Overrides:
nextLong in class Random
Returns:
the next pseudorandom, uniformly distributed long value from this random number generator's sequence

nextLong
public long nextLong
(long bound)
Returns a pseudorandomly chosen long value between zero (inclusive) and the specified bound (exclusive).
Specified by:
nextLong in interface RandomGenerator
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).
Specified by:
nextLong in interface RandomGenerator
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
()
Returns the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextFloat is that one float value, chosen (approximately) uniformly from the range 0.0f (inclusive) to 1.0f (exclusive), is pseudorandomly generated and returned. All 224 possible float values of the form m x 2-24, where m is a positive integer less than 224, are produced with (approximately) equal probability.

Specified by:
nextFloat in interface RandomGenerator
Overrides:
nextFloat in class Random
Returns:
the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence

nextFloat
public float nextFloat
(float bound)
Returns a pseudorandomly chosen float value between zero (inclusive) and the specified bound (exclusive).
Specified by:
nextFloat in interface RandomGenerator
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).
Specified by:
nextFloat in interface RandomGenerator
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
()
Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence.

The general contract of nextDouble is that one double value, chosen (approximately) uniformly from the range 0.0d (inclusive) to 1.0d (exclusive), is pseudorandomly generated and returned.

Specified by:
nextDouble in interface RandomGenerator
Overrides:
nextDouble in class Random
Returns:
the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence
See Also:
Math.random()

nextDouble
public double nextDouble
(double bound)
Returns a pseudorandomly chosen double value between zero (inclusive) and the specified bound (exclusive).
Specified by:
nextDouble in interface RandomGenerator
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).
Specified by:
nextDouble in interface RandomGenerator
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().

Implementation Note:
This method is implemented to be equivalent to ints(Long.MAX_VALUE).
Specified by:
ints in interface RandomGenerator
Overrides:
ints in class Random
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;
   }
 }
Implementation Note:
This method is implemented to be equivalent to ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).
Specified by:
ints in interface RandomGenerator
Overrides:
ints in class Random
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().

Implementation Note:
This method is implemented to be equivalent to longs(Long.MAX_VALUE).
Specified by:
longs in interface RandomGenerator
Overrides:
longs in class Random
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;
 }
Implementation Note:
This method is implemented to be equivalent to longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).
Specified by:
longs in interface RandomGenerator
Overrides:
longs in class Random
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().

Implementation Note:
This method is implemented to be equivalent to doubles(Long.MAX_VALUE).
Specified by:
doubles in interface RandomGenerator
Overrides:
doubles in class Random
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).

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

 
 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;
 }
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).

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

 
 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;
 }
Implementation Note:
This method is implemented to be equivalent to doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound).
Specified by:
doubles in interface RandomGenerator
Overrides:
doubles in class Random
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 greater than or equal to randomNumberBound
Since:
1.8

 Class 
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