Java tutorial
/* * 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: 780975 $ $Date: 2009-06-02 11:05:37 +0200 (mar. 02 juin 2009) $ */ 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); }