Package 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

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      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.
      java.lang.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.
      java.lang.Object[] nextSample​(java.util.Collection<?> c, int k)
      Returns an array of k objects selected randomly from the Collection c.
      java.lang.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

        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.)

        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

        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.)

        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

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