ThreadLocalRandom

public class ThreadLocalRandom
extends Random

java.lang.Object
   ↳ java.util.Random
     ↳ java.util.concurrent.ThreadLocalRandom


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.

Summary

Public methods

static ThreadLocalRandom current()

Returns the current thread's ThreadLocalRandom object.

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).

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()

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).

IntStream ints(long streamSize)

Returns a stream producing the given streamSize number 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()

Returns an effectively unlimited stream 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(long streamSize)

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

LongStream longs()

Returns an effectively unlimited stream 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).

boolean nextBoolean()

Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence.

double nextDouble()

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)

double nextDouble(double origin, double bound)

float nextFloat(float origin, float bound)

float nextFloat()

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)

int nextInt(int origin, int bound)

int nextInt()

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.

long nextLong(long origin, long bound)

long nextLong(long bound)

long nextLong()

Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence.

void setSeed(long seed)

Throws UnsupportedOperationException.

Protected methods

int next(int bits)

Generates a pseudorandom number with the indicated number of low-order bits.

Inherited methods

Public methods

current

Added in API level 21
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
ThreadLocalRandom the current thread's ThreadLocalRandom

doubles

Added in API level 24
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;
 }

Parameters
streamSize long: the number of values to generate

randomNumberOrigin double: the origin (inclusive) of each random value

randomNumberBound double: the bound (exclusive) of each random value

Returns
DoubleStream a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

doubles

Added in API level 24
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 nextDouble().

Parameters
streamSize long: the number of values to generate

Returns
DoubleStream a stream of double values

Throws
IllegalArgumentException

doubles

Added in API level 24
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 nextDouble().

Implementation Note:
  • This method is implemented to be equivalent to doubles(Long.MAX_VALUE).
Returns
DoubleStream a stream of pseudorandom double values

doubles

Added in API level 24
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).
Parameters
randomNumberOrigin double: the origin (inclusive) of each random value

randomNumberBound double: the bound (exclusive) of each random value

Returns
DoubleStream a stream of pseudorandom double values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

ints

Added in API level 24
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 nextInt().

Parameters
streamSize long: the number of values to generate

Returns
IntStream a stream of pseudorandom int values

Throws
IllegalArgumentException

ints

Added in API level 24
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).
Parameters
randomNumberOrigin int: the origin (inclusive) of each random value

randomNumberBound int: the bound (exclusive) of each random value

Returns
IntStream a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

ints

Added in API level 24
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 nextInt().

Implementation Note:
  • This method is implemented to be equivalent to ints(Long.MAX_VALUE).
Returns
IntStream a stream of pseudorandom int values

ints

Added in API level 24
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;
   }
 }

Parameters
streamSize long: the number of values to generate

randomNumberOrigin int: the origin (inclusive) of each random value

randomNumberBound int: the bound (exclusive) of each random value

Returns
IntStream a stream of pseudorandom int values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

longs

Added in API level 24
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 nextLong().

Parameters
streamSize long: the number of values to generate

Returns
LongStream a stream of pseudorandom long values

Throws
IllegalArgumentException

longs

Added in API level 24
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 nextLong().

Implementation Note:
  • This method is implemented to be equivalent to longs(Long.MAX_VALUE).
Returns
LongStream a stream of pseudorandom long values

longs

Added in API level 24
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).
Parameters
randomNumberOrigin long: the origin (inclusive) of each random value

randomNumberBound long: the bound (exclusive) of each random value

Returns
LongStream a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

longs

Added in API level 24
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;
 }

Parameters
streamSize long: the number of values to generate

randomNumberOrigin long: the origin (inclusive) of each random value

randomNumberBound long: the bound (exclusive) of each random value

Returns
LongStream a stream of pseudorandom long values, each with the given origin (inclusive) and bound (exclusive)

Throws
IllegalArgumentException

nextBoolean

Added in API level 21
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.

Returns
boolean the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence

nextDouble

Added in API level 21
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.

Returns
double the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence

nextDouble

Added in API level 21
public double nextDouble (double bound)

Implementation Note:
Parameters
bound double

Returns
double

Throws
IllegalArgumentException

nextDouble

Added in API level 21
public double nextDouble (double origin, 
                double bound)

Implementation Note:
Parameters
origin double

bound double

Returns
double

Throws
IllegalArgumentException

nextFloat

public float nextFloat (float origin, 
                float bound)

Implementation Note:
Parameters
origin float

bound float

Returns
float

Throws
IllegalArgumentException

nextFloat

Added in API level 21
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.

Returns
float 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)

Implementation Note:
Parameters
bound float

Returns
float

Throws
IllegalArgumentException

nextInt

Added in API level 21
public int nextInt (int origin, 
                int bound)

Parameters
origin int

bound int

Returns
int

Throws
IllegalArgumentException

nextInt

Added in API level 21
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.

Returns
int the next pseudorandom, uniformly distributed int value from this random number generator's sequence

nextInt

Added in API level 21
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.

Parameters
bound int: the upper bound (exclusive). Must be positive.

Returns
int the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

Throws
IllegalArgumentException

nextLong

Added in API level 21
public long nextLong (long origin, 
                long bound)

Parameters
origin long

bound long

Returns
long

Throws
IllegalArgumentException

nextLong

Added in API level 21
public long nextLong (long bound)

Parameters
bound long

Returns
long

Throws
IllegalArgumentException

nextLong

Added in API level 21
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.

Returns
long the next pseudorandom, uniformly distributed long value from this random number generator's sequence

setSeed

Added in API level 21
public void setSeed (long seed)

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

Parameters
seed long: the initial seed

Throws
UnsupportedOperationException always

Protected methods

next

Added in API level 21
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.

Parameters
bits int: random bits

Returns
int the next pseudorandom value from this random number generator's sequence