| java.lang.Object
 org.apache.commons.math.random.RandomDataImpl
| RandomDataImpl | | public class RandomDataImpl implements RandomData,Serializable(Code) | | Implements the
RandomData interface using a
RandomGenerator instance to generate non-secure data and a
java.security.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
java.util.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
java.util.Random and
java.security.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
andSecureRandom 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: 348519 $ $Date: 2005-11-23 12:12:18 -0700 (Wed, 23 Nov 2005) $ |
| Method Summary | |
| public double | nextExponential(double mean)
Returns a random value from an Exponential distribution with the given
mean. | | public double | nextGaussian(double mu, double sigma)
Generate a random value from a Normal (a.k.a. | | public String | nextHexString(int len)
Algorithm Description: hex strings are generated
using a 2-step process. | | public int | nextInt(int lower, int upper)
Generate a random int value uniformly distributed between
lower and upper, inclusive.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. | | public long | nextLong(long lower, long upper)
Generate a random long value uniformly distributed between
lower and upper, inclusive.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. | | public int[] | nextPermutation(int n, int k)
Uses a 2-cycle permutation shuffle to generate a random permutation.
The shuffling process is described
here.
Parameters:
n - the population size.
Parameters:
k - the number to choose. | | 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.
Parameters:
mean - mean of the Poisson distribution. | | 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
Parameters:
c - Collection to sample from.
Parameters:
k - sample size. | | public String | nextSecureHexString(int len)
Algorithm Description: hex strings are generated in
40-byte segments using a 3-step process. | | public int | nextSecureInt(int lower, int upper)
Generate a random int value uniformly distributed between
lower and upper, inclusive. | | public long | nextSecureLong(long lower, long upper)
Generate a random long value uniformly distributed between
lower and upper, inclusive. | | 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).
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. | | public void | reSeed(long seed)
Reseeds the random number generator with the supplied seed. | | public void | reSeed()
Reseeds the random number generator with the current time
in milliseconds. | | public void | reSeedSecure()
Reseeds the secure random number generator with the current time
in milliseconds. | | public void | reSeedSecure(long seed)
Reseeds the secure random number generator with the supplied seed. | | public void | setSecureAlgorithm(String algorithm, String provider)
Sets the PRNG algorithm for the underlying SecureRandom instance
using the Security Provider API. |
| RandomDataImpl | | public RandomDataImpl()(Code) | | Construct a RandomDataImpl.
|
| RandomDataImpl | | public RandomDataImpl(RandomGenerator rand)(Code) | | 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 |
| nextExponential | | public double nextExponential(double mean)(Code) | | 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.
Parameters:
mean - the mean of the distribution the random Exponential value |
| nextGaussian | | public double nextGaussian(double mu, double sigma)(Code) | | Generate a random value from a Normal (a.k.a. Gaussian) distribution
with the given mean, mu and the given standard deviation,
sigma.
Parameters:
mu - the mean of the distribution
Parameters:
sigma - the standard deviation of the distribution the random Normal value |
| nextHexString | | public String nextHexString(int len)(Code) | | Algorithm Description: hex strings are generated
using a 2-step process.
-
len/2+1 binary bytes are generated using the underlying Random
-
Each binary byte is translated into 2 hex digits
Parameters:
len - the desired string length. the random string. |
| nextInt | | public int nextInt(int lower, int upper)(Code) | | Generate a random int value uniformly distributed between
lower and upper, inclusive.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. the random integer. |
| nextLong | | public long nextLong(long lower, long upper)(Code) | | Generate a random long value uniformly distributed between
lower and upper, inclusive.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. the random integer. |
| nextPermutation | | public int[] nextPermutation(int n, int k)(Code) | | Uses a 2-cycle permutation shuffle to generate a random permutation.
The shuffling process is described
here.
Parameters:
n - the population size.
Parameters:
k - the number to choose. the random permutation. |
| nextPoisson | | public long nextPoisson(double mean)(Code) | | 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.
Parameters:
mean - mean of the Poisson distribution. the random Poisson value. |
| nextSample | | public Object[] nextSample(Collection c, int k)(Code) | | 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
Parameters:
c - Collection to sample from.
Parameters:
k - sample size. the random sample. |
| nextSecureHexString | | public String nextSecureHexString(int len)(Code) | | Algorithm Description: hex strings are generated in
40-byte segments using a 3-step process.
-
20 random bytes are generated using the underlying
SecureRandom.
-
SHA-1 hash is applied to yield a 20-byte binary digest.
-
Each byte of the binary digest is converted to 2 hex digits.
Parameters:
len - the length of the generated string the random string |
| nextSecureInt | | public int nextSecureInt(int lower, int upper)(Code) | | Generate a random int value uniformly distributed between
lower and upper, inclusive. This algorithm
uses a secure random number generator.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. the random integer. |
| nextSecureLong | | public long nextSecureLong(long lower, long upper)(Code) | | Generate a random long value uniformly distributed between
lower and upper, inclusive. This algorithm
uses a secure random number generator.
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. the random integer. |
| nextUniform | | public double nextUniform(double lower, double upper)(Code) | | 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).
Parameters:
lower - the lower bound.
Parameters:
upper - the upper bound. a uniformly distributed random value from the interval (lower, upper) |
| reSeed | | public void reSeed(long seed)(Code) | | Reseeds the random number generator with the supplied seed.
Will create and initialize if null.
Parameters:
seed - the seed value to use |
| reSeed | | public void reSeed()(Code) | | Reseeds the random number generator with the current time
in milliseconds.
|
| reSeedSecure | | public void reSeedSecure()(Code) | | Reseeds the secure random number generator with the current time
in milliseconds.
Will create and initialize if null.
|
| reSeedSecure | | public void reSeedSecure(long seed)(Code) | | Reseeds the secure random number generator with the supplied seed.
Will create and initialize if null.
Parameters:
seed - the seed value to use |
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