## org.apache.commons.math.random
Class RandomDataImpl

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

All Implemented Interfaces:
  java.io.Serializable, RandomData

    public class RandomDataImpl

extends java.lang.Object
implements RandomData, java.io.Serializable

Implements the `RandomData` interface using a `RandomGenerator` instance to generate non-secure data and a `SecureRandom` instance to provide data for the `nextSecureXxx` methods. If no `RandomGenerator` is provided in the constructor, the default is to use a generator based on `Random`. To plug in a different implementation, either implement `RandomGenerator` directly or extend `AbstractRandomGenerator`.

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 default PRNGs, see `Random` and `SecureRandom`.

Usage Notes:

- Instance variables are used to maintain `RandomGenerator` 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. If you do not explicitly seed the default non-secure generator, it is seeded with the current time in milliseconds on first use. The same holds for the secure generator. If you provide a `RandomGenerator` to the constructor, however, this generator is not reseeded by the constructor nor is it reseeded on first use.
- The `reSeed` and `reSeedSecure` methods delegate to the corresponding methods on the underlying `RandomGenerator` and `SecureRandom` instances. Therefore, `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: 831510 $ $Date: 2009-10-30 22:30:18 -0400 (Fri, 30 Oct 2009) $
See Also:
  Serialized Form

Field Summary
`private RandomGenerator` `rand` underlying random number generator
`private java.security.SecureRandom` `secRand` underlying secure random number generator
`private static long` `serialVersionUID` Serializable version identifier

Constructor Summary
`RandomDataImpl()` Construct a RandomDataImpl.
`RandomDataImpl(RandomGenerator rand)` Construct a RandomDataImpl using the supplied `RandomGenerator` as the source of (non-secure) random data.

Method Summary
`private int[]` `getNatural(int n)` Returns an array representing n.
`private RandomGenerator` `getRan()` Returns the RandomGenerator used to generate non-secure random data.
`private java.security.SecureRandom` `getSecRan()` Returns the SecureRandom used to generate secure random data.
`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.
`java.lang.String` `nextHexString(int len)` Generates a random string of hex characters of length `len`.
`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)` Generates an integer array of length `k` whose entries are selected randomly, without repetition, from the integers `0 through n-1` (inclusive).
`long` `nextPoisson(double mean)` Generates a random value from the Poisson distribution with the given mean.
`java.lang.Object[]` `nextSample(java.util.Collection<?> c, int k)` Uses a 2-cycle permutation shuffle to generate a random permutation.
`java.lang.String` `nextSecureHexString(int len)` Generates a random string of hex characters from a secure random sequence.
`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)` Generates a uniformly distributed random value from the open interval (`lower`,`upper`) (i.e., endpoints excluded).
`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(java.lang.String algorithm, java.lang.String provider)` Sets the PRNG algorithm for the underlying SecureRandom instance using the Security Provider API.
`private void` `shuffle(int[] list, int end)` Uses a 2-cycle permutation shuffle to randomly re-order the last elements of list.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### serialVersionUID

    private static final long serialVersionUID

  Serializable version identifier

  See Also:
    Constant Field Values

### rand

    private RandomGenerator rand

  underlying random number generator

### secRand

    private java.security.SecureRandom secRand

  underlying secure random number generator

Constructor Detail

### RandomDataImpl

    public RandomDataImpl()

  Construct a RandomDataImpl.

### RandomDataImpl

    public RandomDataImpl(RandomGenerator rand)

  Construct a RandomDataImpl using the supplied `RandomGenerator` as the source of (non-secure) random data.

  Parameters:
    `rand` - the source of (non-secure) random data
  Since:
    1.1

Method Detail

### nextHexString

    public java.lang.String nextHexString(int len)

  Generates a random string of hex characters of length `len`.

  The generated string will be random, but not cryptographically secure. To generate cryptographically secure strings, use `nextSecureHexString`

  Preconditions:

  - `len > 0` (otherwise an IllegalArgumentException is thrown.)

  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 java.lang.String nextSecureHexString(int len)

  Generates a random string of hex characters from a secure random sequence.

  If cryptographic security is not required, use `nextHexString()`.

  Preconditions:

  - `len > 0` (otherwise an IllegalArgumentException is thrown.)

  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 value from the Poisson distribution with the given mean.

  Definition: Poisson Distribution

  Preconditions:

  - The specified mean must be positive (otherwise an IllegalArgumentException is thrown.)

  Algorithm Description:

  - For small means, uses simulation of a Poisson process using Uniform deviates, as described here. The Poisson process (and hence value returned) is bounded by 1000 * mean.
  - For large means, uses the rejection algorithm described in
    Devroye, Luc. (1981).The Computer Generation of Poisson Random Variables Computing vol. 26 pp. 197-207.

  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)

  Generates a uniformly distributed random value from the open interval (`lower`,`upper`) (i.e., endpoints excluded).

  Definition: Uniform Distribution `lower` and `upper - lower` are the location and scale parameters, respectively.

  Preconditions:

  - `lower < upper` (otherwise an IllegalArgumentException is thrown.)

  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:
    a uniformly distributed random value from the interval (lower, upper)

### getRan

    private RandomGenerator getRan()

  Returns the RandomGenerator used to generate non-secure random data.

  Creates and initializes a default generator if null.

  Returns:
    the Random used to generate random data
  Since:
    1.1

### getSecRan

    private java.security.SecureRandom getSecRan()

  Returns the SecureRandom used to generate secure random data.

  Creates and initializes if null.

  Returns:
    the SecureRandom used to generate secure random data

### 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(java.lang.String algorithm,
                                   java.lang.String provider)
                            throws java.security.NoSuchAlgorithmException,
                                   java.security.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:
    `java.security.NoSuchAlgorithmException` - if the specified algorithm is not available
    `java.security.NoSuchProviderException` - if the specified provider is not installed

### nextPermutation

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

  Generates an integer array of length `k` whose entries are selected randomly, without repetition, from the integers `0 through n-1` (inclusive).

  Generated arrays represent permutations of `n` taken `k` at a time.

  Preconditions:

  - `k <= n`
  - `n > 0`
  If the preconditions are not met, an IllegalArgumentException is thrown.

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

  Specified by:
    `nextPermutation` in interface `RandomData`
  Parameters:
    `n` - domain of the permutation (must be positive)
    `k` - size of the permutation (must satisfy 0 < k <= n).
  Returns:
    the random permutation as an int array

### nextSample

    public java.lang.Object[] nextSample(java.util.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.

### shuffle

    private void shuffle(int[] list,
                         int end)

  Uses a 2-cycle permutation shuffle to randomly re-order the last elements of list.

  Parameters:
    `list` - list to be shuffled
    `end` - element past which shuffling begins

### getNatural

    private int[] getNatural(int n)

  Returns an array representing n.

  Parameters:
    `n` - the natural number to represent
  Returns:
    array with entries = elements of n

Copyright (c) 2003-2011 Apache Software Foundation