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TOVAL comprises a set of java classes for common programming issues. It includes utils for arrays, lists, sets and collections for convenient handling and modification, but also support for mathematic definitions concerning logic (clauses + resolution) together with some algorithms for permutations, powersets and resolution. Additionally it contains a number of types for multisets, matrices with object keys and much more.

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/*
 * Copyright (c) 2015, Thomas Stocker
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted (subject to the limitations in the disclaimer
 * below) provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * * Neither the name of IIG Telematics, Uni Freiburg nor the names of its
 *   contributors may be used to endorse or promote products derived from this
 *   software without specific prior written permission.
 *
 * NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED BY
 * THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BELIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package de.invation.code.toval.misc;

import java.util.Random;

/**
 *
 * @author Thomas Stocker
 *
 */
public class RandomUtils {

    private static final java.util.Random rand = new Random();

    /**
     * Returns a random positive double value in the range [0;1).
     *
     * @return Random double value in the range [0;1)
     */
    public static double randomPosDouble() {
        return Math.abs(rand.nextDouble());
    }

    /**
     * Returns a random negative double value in the range (-1;0].
     *
     * @return Random double value in the range (-1;0]
     */
    public static double randomNegDouble() {
        return -randomPosDouble();
    }

    /**
     * Returns a random int value out of a specified range
     *
     * @param lowerBound Lower bound of the target range (inclusive)
     * @param upperBound Upper bound of the target range (exclusive)
     * @return A random int value out of a specified range
     */
    public static int randomIntBetween(int lowerBound, int upperBound) {
        if (upperBound < lowerBound) {
            throw new IllegalArgumentException("lower bound higher than upper bound");
        }
        return rand.nextInt(upperBound - lowerBound) + lowerBound;
    }

    /**
     * Returns a random long value out of a specified range
     *
     * @param lowerBound Lower bound of the target range (inclusive)
     * @param upperBound Upper bound of the target range (exclusive)
     * @return A random long value out of a specified range
     */
    public static long randomLongBetween(long lowerBound, long upperBound) {
        if (upperBound < lowerBound) {
            throw new IllegalArgumentException("lower bound higher than upper bound");
        }
        return lowerBound + (long) (rand.nextDouble() * (upperBound - lowerBound));
    }

    /**
     * A random string generator.
     */
    public static class RandomStringGenerator {

        private final char[] symbols;

        private final Random random = new Random();

        private final char[] buf;

        /**
         * Creates a new RandomStringGenerator of the specified length.
         *
         * @param length Length of the random strings, must be larger than 1.
         * @param includeNumericSymbols
         * @param includeLowerCaseLetters
         * @param includeUpperCaseLetters
         */
        public RandomStringGenerator(int length, boolean includeNumericSymbols, boolean includeLowerCaseLetters, boolean includeUpperCaseLetters) {
            if (length < 1) {
                throw new IllegalArgumentException("length < 1: " + length);
            }
            buf = new char[length];

            StringBuilder tmp = new StringBuilder();
            for (char ch = '0'; includeNumericSymbols && ch <= '9'; ++ch) {
                tmp.append(ch);
            }
            for (char ch = 'a'; includeLowerCaseLetters && ch <= 'z'; ++ch) {
                tmp.append(ch);
            }
            for (char ch = 'A'; includeUpperCaseLetters && ch <= 'Z'; ++ch) {
                tmp.append(ch);
            }
            symbols = tmp.toString().toCharArray();
        }

        /**
         * Returns the next random string.
         *
         * @return A random string
         */
        public String nextString() {
            for (int idx = 0; idx < buf.length; ++idx) {
                buf[idx] = symbols[random.nextInt(symbols.length)];
            }
            return new String(buf);
        }
    }
}