Package java.util

Class Random

java.lang.Object

java.util.Random

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

SecureRandom, ThreadLocalRandom

public class Random
extends Object
implements Serializable

This class provides methods that return pseudo-random values.

It is dangerous to seed Random with the current time because that value is more predictable to an attacker than the default seed.

This class is thread-safe.

See Also:

SecureRandom, Serialized Form

Constructor Summary

Constructors

Constructor	Description
Random()	Constructs a random generator with an initial state that is unlikely to be duplicated by a subsequent instantiation.
Random(long seed)	Construct a random generator with the given seed as the initial state.

Method Summary

Modifier and Type	Method	Description
protected int	next(int bits)	Returns a pseudo-random uniformly distributed int value of the number of bits specified by the argument bits as described by Donald E.
boolean	nextBoolean()	Returns a pseudo-random uniformly distributed boolean.
void	nextBytes(byte[] buf)	Fills buf with random bytes.
double	nextDouble()	Returns a pseudo-random uniformly distributed double in the half-open range [0.0, 1.0).
float	nextFloat()	Returns a pseudo-random uniformly distributed float in the half-open range [0.0, 1.0).
double	nextGaussian()	Returns a pseudo-random (approximately) normally distributed double with mean 0.0 and standard deviation 1.0.
int	nextInt()	Returns a pseudo-random uniformly distributed int.
int	nextInt(int n)	Returns a pseudo-random uniformly distributed int in the half-open range [0, n).
long	nextLong()	Returns a pseudo-random uniformly distributed long.
void	setSeed(long seed)	Modifies the seed using a linear congruential formula presented in The Art of Computer Programming, Volume 2, Section 3.2.1.

Methods inherited from class java.lang.Object

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

Constructor Detail

Random

public Random()

Constructs a random generator with an initial state that is unlikely to be duplicated by a subsequent instantiation.

Random

public Random(long seed)

Construct a random generator with the given seed as the initial state. Equivalent to Random r = new Random(); r.setSeed(seed);.

This constructor is mainly useful for predictability in tests. The default constructor is likely to provide better randomness.

Method Detail

next

protected int next(int bits)

Returns a pseudo-random uniformly distributed int value of the number of bits specified by the argument bits as described by Donald E. Knuth in The Art of Computer Programming, Volume 2: Seminumerical Algorithms, section 3.2.1.

Most applications will want to use one of this class' convenience methods instead.

Subclasses only need to override this method to alter the behavior of all the public methods.

nextBoolean

public boolean nextBoolean()

Returns a pseudo-random uniformly distributed boolean.

nextBytes

public void nextBytes(byte[] buf)

Fills buf with random bytes.

nextDouble

public double nextDouble()

Returns a pseudo-random uniformly distributed double in the half-open range [0.0, 1.0).

nextFloat

public float nextFloat()

Returns a pseudo-random uniformly distributed float in the half-open range [0.0, 1.0).

nextGaussian

public double nextGaussian()

Returns a pseudo-random (approximately) normally distributed double with mean 0.0 and standard deviation 1.0. This method uses the polar method of G. E. P. Box, M. E. Muller, and G. Marsaglia, as described by Donald E. Knuth in The Art of Computer Programming, Volume 2: Seminumerical Algorithms, section 3.4.1, subsection C, algorithm P.

nextInt

public int nextInt()

Returns a pseudo-random uniformly distributed int.

nextInt

public int nextInt(int n)

Returns a pseudo-random uniformly distributed int in the half-open range [0, n).

nextLong

public long nextLong()

Returns a pseudo-random uniformly distributed long.

setSeed

public void setSeed(long seed)

Modifies the seed using a linear congruential formula presented in The Art of Computer Programming, Volume 2, Section 3.2.1.