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## org.apache.commons.math.random
Interface RandomData

All Known Implementing Classes:
  RandomDataImpl

    public interface RandomData

Random data generation utilities.

Version:
  $Revision: 780975 $ $Date: 2009-06-02 11:05:37 +0200 (mar. 02 juin 2009) $

Method Summary
`double` | `nextExponential(double mean)` Generates a random value from the exponential distribution with expected value = `mean`.
`double` | `nextGaussian(double mu, double sigma)` Generates a random value from the Normal (or Gaussian) distribution with the given mean and standard deviation.
`String` | `nextHexString(int len)` Generates a random string of hex characters of length `len`.
`int` | `nextInt(int lower, int upper)` Generates a uniformly distributed random integer between `lower` and `upper` (endpoints included).
`long` | `nextLong(long lower, long upper)` Generates a uniformly distributed random long integer between `lower` and `upper` (endpoints included).
`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.
`Object[]` | `nextSample(Collection<?> c, int k)` Returns an array of `k` objects selected randomly from the Collection `c`.
`String` | `nextSecureHexString(int len)` Generates a random string of hex characters from a secure random sequence.
`int` | `nextSecureInt(int lower, int upper)` Generates a uniformly distributed random integer between `lower` and `upper` (endpoints included) from a secure random sequence.
`long` | `nextSecureLong(long lower, long upper)` Generates a random long integer between `lower` and `upper` (endpoints included).
`double` | `nextUniform(double lower, double upper)` Generates a uniformly distributed random value from the open interval (`lower`,`upper`) (i.e., endpoints excluded).

Method Detail

### nextHexString

    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.)

  Parameters:
    `len` - the length of the string to be generated
  Returns:
    random string of hex characters of length `len`

### nextInt

    int nextInt(int lower,
                int upper)

  Generates a uniformly distributed random integer between `lower` and `upper` (endpoints included).

  The generated integer will be random, but not cryptographically secure. To generate cryptographically secure integer sequences, use `nextSecureInt`.

  Preconditions:

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

  Parameters:
    `lower` - lower bound for generated integer
    `upper` - upper bound for generated integer
  Returns:
    a random integer greater than or equal to `lower` and less than or equal to `upper`.

### nextLong

    long nextLong(long lower,
                  long upper)

  Generates a uniformly distributed random long integer between `lower` and `upper` (endpoints included).

  The generated long integer values will be random, but not cryptographically secure. To generate cryptographically secure sequences of longs, use `nextSecureLong`

  Preconditions:

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

  Parameters:
    `lower` - lower bound for generated integer
    `upper` - upper bound for generated integer
  Returns:
    a random integer greater than or equal to `lower` and less than or equal to `upper`.

### nextSecureHexString

    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.)

  Parameters:
    `len` - length of return string
  Returns:
    the random hex string

### nextSecureInt

    int nextSecureInt(int lower,
                      int upper)

  Generates a uniformly distributed random integer between `lower` and `upper` (endpoints included) from a secure random sequence.

  Sequences of integers generated using this method will be cryptographically secure. If cryptographic security is not required, `nextInt` should be used instead of this method.

  Definition: Secure Random Sequence

  Preconditions:

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

  Parameters:
    `lower` - lower bound for generated integer
    `upper` - upper bound for generated integer
  Returns:
    a random integer greater than or equal to `lower` and less than or equal to `upper`.

### nextSecureLong

    long nextSecureLong(long lower,
                        long upper)

  Generates a random long integer between `lower` and `upper` (endpoints included).

  Sequences of long values generated using this method will be cryptographically secure. If cryptographic security is not required, `nextLong` should be used instead of this method.

  Definition: Secure Random Sequence

  Preconditions:

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

  Parameters:
    `lower` - lower bound for generated integer
    `upper` - upper bound for generated integer
  Returns:
    a long integer greater than or equal to `lower` and less than or equal to `upper`.

### nextPoisson

    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.)

  Parameters:
    `mean` - Mean of the distribution
  Returns:
    poisson deviate with the specified mean

### nextGaussian

    double nextGaussian(double mu,
                        double sigma)

  Generates a random value from the Normal (or Gaussian) distribution with the given mean and standard deviation.

  Definition: Normal Distribution

  Preconditions:

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

  Parameters:
    `mu` - Mean of the distribution
    `sigma` - Standard deviation of the distribution
  Returns:
    random value from Gaussian distribution with mean = mu, standard deviation = sigma

### nextExponential

    double nextExponential(double mean)

  Generates a random value from the exponential distribution with expected value = `mean`.

  Definition: Exponential Distribution

  Preconditions:

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

  Parameters:
    `mean` - Mean of the distribution
  Returns:
    random value from exponential distribution

### nextUniform

    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.)

  Parameters:
    `lower` - lower endpoint of the interval of support
    `upper` - upper endpoint of the interval of support
  Returns:
    uniformly distributed random value between lower and upper (exclusive)

### nextPermutation

    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.

  Parameters:
    `n` - domain of the permutation
    `k` - size of the permutation
  Returns:
    random k-permutation of n

### nextSample

    Object[] nextSample(Collection<?> c,
                        int k)

  Returns an array of `k` objects selected randomly from the Collection `c`.

  Sampling from `c` is without replacement; but if `c` contains identical objects, the sample may include repeats. If all elements of `c` are distinct, the resulting object array represents a Simple Random Sample of size `k` from the elements of `c`.

  Preconditions:

  - k must be less than or equal to the size of c
  - c must not be empty
  If the preconditions are not met, an IllegalArgumentException is thrown.

  Parameters:
    `c` - collection to be sampled
    `k` - size of the sample
  Returns:
    random sample of k elements from c

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