/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements.  See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License.  You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.apache.commons.math.random;import java.util.Collection;/** * Random data generation utilities. * @version $Revision: 615734 $ $Date: 2008-01-27 23:10:03 -0700 (Sun, 27 Jan 2008) $ */public interface RandomData {    /**     * Generates a random string of hex characters of length     * <code>len</code>.     * <p>     * The generated string will be random, but not cryptographically     * secure. To generate cryptographically secure strings, use     * <code>nextSecureHexString</code></p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>len > 0</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param len the length of the string to be generated     * @return random string of hex characters of length <code>len</code>     */    String nextHexString(int len);    /**     * Generates a uniformly distributed random integer between     * <code>lower</code> and <code>upper</code> (endpoints included).     * <p>     * The generated integer will be random, but not cryptographically secure.     * To generate cryptographically secure integer sequences, use     * <code>nextSecureInt</code>.</p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>lower < upper</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param lower lower bound for generated integer     * @param upper upper bound for generated integer     * @return a random integer greater than or equal to <code>lower</code>     * and less than or equal to <code>upper</code>.     */    int nextInt(int lower, int upper);    /**     * Generates a uniformly distributed random long integer between     * <code>lower</code> and <code>upper</code> (endpoints included).     * <p>     * The generated long integer values will be random, but not     * cryptographically secure.     * To generate cryptographically secure sequences of longs, use     * <code>nextSecureLong</code></p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>lower < upper</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param lower lower bound for generated integer     * @param upper upper bound for generated integer     * @return a random integer greater than or equal to <code>lower</code>     * and less than or equal to <code>upper</code>.     */    long nextLong(long lower, long upper);    /**     * Generates a random string of hex characters from a secure random     * sequence.     * <p>     * If cryptographic security is not required,     * use <code>nextHexString()</code>.</p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>len > 0</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     * @param len length of return string     * @return the random hex string     */    String nextSecureHexString(int len);    /**     * Generates a uniformly distributed random integer between     * <code>lower</code> and <code>upper</code> (endpoints included)     * from a secure random sequence.     * <p>     * Sequences of integers generated using this method will be     * cryptographically secure. If cryptographic security is not required,     * <code>nextInt</code> should be used instead of this method.</p>     * <p>     * <strong>Definition</strong>:     * <a href="http://en.wikipedia.org/wiki/Cryptographically_secure_pseudo-random_number_generator">     * Secure Random Sequence</a></p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>lower < upper</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param lower lower bound for generated integer     * @param upper upper bound for generated integer     * @return a random integer greater than or equal to <code>lower</code>     * and less than or equal to <code>upper</code>.     */    int nextSecureInt(int lower, int upper);    /**     * Generates a random long integer between <code>lower</code>     * and <code>upper</code> (endpoints included).     * <p>     * Sequences of long values generated using this method will be     * cryptographically secure. If cryptographic security is not required,     * <code>nextLong</code> should be used instead of this method.</p>     * <p>     * <strong>Definition</strong>:     * <a href="http://en.wikipedia.org/wiki/Cryptographically_secure_pseudo-random_number_generator">     * Secure Random Sequence</a></p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>lower < upper</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param lower lower bound for generated integer     * @param upper upper bound for generated integer     * @return a long integer greater than or equal to <code>lower</code>     * and less than or equal to <code>upper</code>.     */    long nextSecureLong(long lower, long upper);    /**     * Generates a random value from the Poisson distribution with     * the given mean.     * <p>     * <strong>Definition</strong>:     * <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda366j.htm">     * Poisson Distribution</a></p>     * <p>     * <strong>Preconditions</strong>: <ul>     * <li>The specified mean <i>must</i> be positive (otherwise an     *     IllegalArgumentException is thrown.)</li>     * </ul></p>     * @param mean Mean of the distribution     * @return poisson deviate with the specified mean     */    long nextPoisson(double mean);    /**     * Generates a random value from the     * Normal (or Gaussian) distribution with the given mean     * and standard deviation.     * <p>     * <strong>Definition</strong>:     * <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3661.htm">     * Normal Distribution</a></p>     * <p>     * <strong>Preconditions</strong>: <ul>     * <li><code>sigma > 0</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     * @param mu Mean of the distribution     * @param sigma Standard deviation of the distribution     * @return random value from Gaussian distribution with mean = mu,     * standard deviation = sigma     */    double nextGaussian(double mu, double sigma);    /**     * Generates a random value from the exponential distribution     * with expected value = <code>mean</code>.     * <p>     * <strong>Definition</strong>:     * <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3667.htm">     * Exponential Distribution</a></p>     * <p>     * <strong>Preconditions</strong>: <ul>     * <li><code>mu >= 0</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     * @param mean Mean of the distribution     * @return random value from exponential distribution     */    double nextExponential(double mean);    /**     * Generates a uniformly distributed random value from the open interval     * (<code>lower</code>,<code>upper</code>) (i.e., endpoints excluded).     * <p>     * <strong>Definition</strong>:     * <a href="http://www.itl.nist.gov/div898/handbook/eda/section3/eda3662.htm">     * Uniform Distribution</a> <code>lower</code> and     * <code>upper - lower</code> are the     * <a href = "http://www.itl.nist.gov/div898/handbook/eda/section3/eda364.htm">     * location and scale parameters</a>, respectively.</p>     * <p>     * <strong>Preconditions</strong>:<ul>     * <li><code>lower < upper</code> (otherwise an IllegalArgumentException     *     is thrown.)</li>     * </ul></p>     *     * @param lower lower endpoint of the interval of support     * @param upper upper endpoint of the interval of support     * @return uniformly distributed random value between lower     * and upper (exclusive)     */    double nextUniform(double lower, double upper);    /**     * Generates an integer array of length <code>k</code> whose entries     * are selected randomly, without repetition, from the integers <code>     * 0 through n-1</code> (inclusive).     * <p>     * Generated arrays represent permutations     * of <code>n</code> taken <code>k</code> at a time.</p>     * <p>     * <strong>Preconditions:</strong><ul>     * <li> <code>k <= n</code></li>     * <li> <code>n > 0</code> </li>     * </ul>     * If the preconditions are not met, an IllegalArgumentException is     * thrown.</p>     *     * @param n domain of the permutation     * @param k size of the permutation     * @return random k-permutation of n     */    int[] nextPermutation(int n, int k);    /**     * Returns an array of <code>k</code> objects selected randomly     * from the Collection <code>c</code>.     * <p>     * Sampling from <code>c</code>     * is without replacement; but if <code>c</code> contains identical     * objects, the sample may include repeats.  If all elements of <code>     * c</code> are distinct, the resulting object array represents a     * <a href="http://rkb.home.cern.ch/rkb/AN16pp/node250.html#SECTION0002500000000000000000">     * Simple Random Sample</a> of size     * <code>k</code> from the elements of <code>c</code>.</p>     * <p>     * <strong>Preconditions:</strong><ul>     * <li> k must be less than or equal to the size of c </li>     * <li> c must not be empty </li>     * </ul>     * If the preconditions are not met, an IllegalArgumentException is     * thrown.</p>     *     * @param c collection to be sampled     * @param k size of the sample     * @return random sample of k elements from c     */    Object[] nextSample(Collection c, int k);}