org.apache.commons.math.random
Class RandomDataImpl

java.lang.Object
  extended byorg.apache.commons.math.random.RandomDataImpl
All Implemented Interfaces:
RandomData, Serializable

public class RandomDataImpl
extends Object
implements RandomData, Serializable

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

Supports reseeding the underlying PRNG. The SecurityProvider and Algorithm used by the SecureRandom instance can also be reset.

For details on the PRNGs, see the JDK documentation for java.util.Random and java.util.Random.SecureRandom

Usage Notes:

Version:
$Revision: 1.9 $ $Date: 2003/11/19 03:28:24 $
See Also:
Serialized Form

Constructor Summary
RandomDataImpl()
          Construct a RandomDataImpl.
 
Method Summary
 double nextExponential(double mean)
          Algorithm Description: Uses the Inversion Method to generate exponential from uniform deviates.
 double nextGaussian(double mu, double sigma)
          Generate a random value from a Normal distribution.
 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)
          Algorithm Description: Uses simulation of a Poisson process using Uniform deviates, as described here
 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
 

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

TODO: find external reference or provide justification for the claim that this yields a cryptographically secure sequence of hex strings.

Specified by:
nextSecureHexString in interface RandomData
Parameters:
len - the desired string length.
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 using a secure random number generator for its engine.

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 using a secure random number generator for its engine.

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

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 distribution. This algorithm generates random values for the general Normal 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)
Algorithm Description: Uses the Inversion Method to generate exponential 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.


Copyright © 2003-2004 Apache Software Foundation. All Rights Reserved.