org.apache.commons.math.random
Class RandomDataImpl

java.lang.Object
  org.apache.commons.math.random.RandomDataImpl

All Implemented Interfaces:

RandomData, Serializable

public class RandomDataImpl

extends Object

implements RandomData, Serializable

Implements the RandomData interface using Random and Random.SecureRandom instances to generate data.

Supports reseeding the underlying pseudo-random number generator (PRNG). The SecurityProvider and Algorithm used by the SecureRandom instance can also be reset.

For details on the PRNGs, see Random and Random.SecureRandom.

Usage Notes:

• Instance variables are used to maintain Random and SecureRandom instances used in data generation. Therefore, to generate a random sequence of values or strings, you should use just one RandomDataImpl instance repeatedly.
• The "secure" methods are *much* slower. These should be used only when a cryptographically secure random sequence is required. A secure random sequence is a sequence of pseudo-random values which, in addition to being well-dispersed (so no subsequence of values is an any more likely than other subsequence of the the same length), also has the additional property that knowledge of values generated up to any point in the sequence does not make it any easier to predict subsequent values.
• When a new RandomDataImpl is created, the underlying random number generators are not intialized. The first call to a data generation method, or to a reSeed() method instantiates the appropriate generator. If you do not explicitly seed the generator, it is by default seeded with the current time in milliseconds
• The reSeed and reSeedSecure methods delegate to the corresponding methods on the underlying Random and SecureRandom instances. Therefore, the contracts of these methods are as defined in the JDK documentation. In particular, reSeed(long) fully resets the initial state of the non-secure random number generator (so that reseeding with a specific value always results in the same subsequent random sequence); whereas reSeedSecure(long) does not reinitialize the secure random number generator (so secure sequences started with calls to reseedSecure(long) won't be identical).
• This implementation is not synchronized.

Version:

$Revision: 1.16 $ $Date: 2004/07/22 02:34:25 $

See Also:

Serialized Form

Field Summary

(package private) static long

serialVersionUID Serializable version identifier

Constructor Summary

RandomDataImpl()
Construct a RandomDataImpl.

Method Summary

double	nextExponential(double mean) Returns a random value from an Exponential distribution with the given mean.
double	nextGaussian(double mu, double sigma) Generate a random value from a Normal (a.k.a.
String	nextHexString(int len) Algorithm Description: hex strings are generated using a 2-step process.
int	nextInt(int lower, int upper) Generate a random int value uniformly distributed between lower and upper, inclusive.
long	nextLong(long lower, long upper) Generate a random long value uniformly distributed between lower and upper, inclusive.
int[]	nextPermutation(int n, int k) Uses a 2-cycle permutation shuffle to generate a random permutation.
long	nextPoisson(double mean) Generates a random long value from the Poisson distribution with the given mean.
Object[]	nextSample(Collection c, int k) Uses a 2-cycle permutation shuffle to generate a random permutation.
String	nextSecureHexString(int len) Algorithm Description: hex strings are generated in 40-byte segments using a 3-step process.
int	nextSecureInt(int lower, int upper) Generate a random int value uniformly distributed between lower and upper, inclusive.
long	nextSecureLong(long lower, long upper) Generate a random long value uniformly distributed between lower and upper, inclusive.
double	nextUniform(double lower, double upper) Algorithm Description: scales the output of Random.nextDouble(), but rejects 0 values (i.e., will generate another random double if Random.nextDouble() returns 0).
void	reSeed() Reseeds the random number generator with the current time in milliseconds.
void	reSeed(long seed) Reseeds the random number generator with the supplied seed.
void	reSeedSecure() Reseeds the secure random number generator with the current time in milliseconds.
void	reSeedSecure(long seed) Reseeds the secure random number generator with the supplied seed.
void	setSecureAlgorithm(String algorithm, String provider) Sets the PRNG algorithm for the underlying SecureRandom instance using the Security Provider API.

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

static final long serialVersionUID

Serializable version identifier

See Also:

Constant Field Values

Constructor Detail

RandomDataImpl

public RandomDataImpl()

Construct a RandomDataImpl.

Method Detail

nextHexString

public String nextHexString(int len)

Algorithm Description: hex strings are generated using a 2-step process.

1. len/2+1 binary bytes are generated using the underlying Random
2. Each binary byte is translated into 2 hex digits

Specified by:

nextHexString in interface RandomData

Parameters:

len - the desired string length.

Returns:

the random string.

nextInt

public int nextInt(int lower,
                   int upper)

Generate a random int value uniformly distributed between lower and upper, inclusive.

Specified by:

nextInt in interface RandomData

Parameters:

lower - the lower bound.

upper - the upper bound.

Returns:

the random integer.

nextLong

public long nextLong(long lower,
                     long upper)

Generate a random long value uniformly distributed between lower and upper, inclusive.

Specified by:

nextLong in interface RandomData

Parameters:

lower - the lower bound.

upper - the upper bound.

Returns:

the random integer.

nextSecureHexString

public String nextSecureHexString(int len)

Algorithm Description: hex strings are generated in 40-byte segments using a 3-step process.

1. 20 random bytes are generated using the underlying SecureRandom.
2. SHA-1 hash is applied to yield a 20-byte binary digest.
3. Each byte of the binary digest is converted to 2 hex digits.

Specified by:

nextSecureHexString in interface RandomData

Parameters:

len - the length of the generated string

Returns:

the random string

nextSecureInt

public int nextSecureInt(int lower,
                         int upper)

Generate a random int value uniformly distributed between lower and upper, inclusive. This algorithm uses a secure random number generator.

Specified by:

nextSecureInt in interface RandomData

Parameters:

lower - the lower bound.

upper - the upper bound.

Returns:

the random integer.

nextSecureLong

public long nextSecureLong(long lower,
                           long upper)

Generate a random long value uniformly distributed between lower and upper, inclusive. This algorithm uses a secure random number generator.

Specified by:

nextSecureLong in interface RandomData

Parameters:

lower - the lower bound.

upper - the upper bound.

Returns:

the random integer.

nextPoisson

public long nextPoisson(double mean)

Generates a random long value from the Poisson distribution with the given mean.

Algorithm Description: Uses simulation of a Poisson process using Uniform deviates, as described here.

The Poisson process (and hence value returned) is bounded by 1000 * mean.

Specified by:

nextPoisson in interface RandomData

Parameters:

mean - mean of the Poisson distribution.

Returns:

the random Poisson value.

nextGaussian

public double nextGaussian(double mu,
                           double sigma)

Generate a random value from a Normal (a.k.a. Gaussian) distribution with the given mean, mu and the given standard deviation, sigma.

Specified by:

nextGaussian in interface RandomData

Parameters:

mu - the mean of the distribution

sigma - the standard deviation of the distribution

Returns:

the random Normal value

nextExponential

public double nextExponential(double mean)

Returns a random value from an Exponential distribution with the given mean.

Algorithm Description: Uses the Inversion Method to generate exponentially distributed random values from uniform deviates.

Specified by:

nextExponential in interface RandomData

Parameters:

mean - the mean of the distribution

Returns:

the random Exponential value

nextUniform

public double nextUniform(double lower,
                          double upper)

Algorithm Description: scales the output of Random.nextDouble(), but rejects 0 values (i.e., will generate another random double if Random.nextDouble() returns 0). This is necessary to provide a symmetric output interval (both endpoints excluded).

Specified by:

nextUniform in interface RandomData

Parameters:

lower - the lower bound.

upper - the upper bound.

Returns:

the random value.

reSeed

public void reSeed(long seed)

Reseeds the random number generator with the supplied seed.

Will create and initialize if null.

Parameters:

seed - the seed value to use

reSeedSecure

public void reSeedSecure()

Reseeds the secure random number generator with the current time in milliseconds.

Will create and initialize if null.

reSeedSecure

public void reSeedSecure(long seed)

Reseeds the secure random number generator with the supplied seed.

Will create and initialize if null.

Parameters:

seed - the seed value to use

reSeed

public void reSeed()

Reseeds the random number generator with the current time in milliseconds.

setSecureAlgorithm

public void setSecureAlgorithm(String algorithm,
                               String provider)
                        throws NoSuchAlgorithmException,
                               NoSuchProviderException

Sets the PRNG algorithm for the underlying SecureRandom instance using the Security Provider API. The Security Provider API is defined in Java Cryptography Architecture API Specification & Reference.

USAGE NOTE: This method carries significant overhead and may take several seconds to execute.

Parameters:

algorithm - the name of the PRNG algorithm

provider - the name of the provider

Throws:

NoSuchAlgorithmException - if the specified algorithm is not available

NoSuchProviderException - if the specified provider is not installed

nextPermutation

public int[] nextPermutation(int n,
                             int k)

Uses a 2-cycle permutation shuffle to generate a random permutation. The shuffling process is described here.

Specified by:

nextPermutation in interface RandomData

Parameters:

n - the population size.

k - the number to choose.

Returns:

the random permutation.

nextSample

public Object[] nextSample(Collection c,
                           int k)

Uses a 2-cycle permutation shuffle to generate a random permutation. Algorithm Description: Uses a 2-cycle permutation shuffle to generate a random permutation of c.size() and then returns the elements whose indexes correspond to the elements of the generated permutation. This technique is described, and proven to generate random samples, here

Specified by:

nextSample in interface RandomData

Parameters:

c - Collection to sample from.

k - sample size.

Returns:

the random sample.