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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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/*
 * 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.lang3;

import java.util.Random;

/**
 * Utility library that supplements the standard {@link Random} class.
 * 
 * @since 3.3
 *
 * @version $Id: RandomUtils.java 1580464 2014-03-23 07:28:42Z djones $
 */
public class RandomUtils {

    /**
     * Random object used by random method. This has to be not local to the
     * random method so as to not return the same value in the same millisecond.
     */
    private static final Random RANDOM = new Random();

    /**
     * 
     * {@code RandomUtils} instances should NOT be constructed in standard
     * programming. Instead, the class should be used as
     * {@code RandomUtils.nextBytes(5);}.
     * 
     * 
     * 
     * This constructor is public to permit tools that require a JavaBean
     * instance to operate.
     * 
     */
    public RandomUtils() {
        super();
    }

    /**
     * 
     * Creates an array of random bytes.
     * 
     * 
     * @param count
     *            the size of the returned array
     * @return the random byte array
     * @throws IllegalArgumentException if {@code count} is negative
     */
    public static byte[] nextBytes(int count) {
        Validate.isTrue(count >= 0, "Count cannot be negative.");

        byte[] result = new byte[count];
        RANDOM.nextBytes(result);
        return result;
    }

    /**
     * 
     * Returns a random integer within the specified range.
     * 
     * 
     * @param startInclusive
     *            the smallest value that can be returned, must be non-negative
     * @param endExclusive
     *            the upper bound (not included)
     * @throws IllegalArgumentException
     *             if {@code startInclusive > endExclusive} or if
     *             {@code startInclusive} is negative
     * @return the random integer
     */
    public static int nextInt(int startInclusive, int endExclusive) {
        Validate.isTrue(endExclusive >= startInclusive,
                "Start value must be smaller or equal to end value.");
        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");

        if (startInclusive == endExclusive) {
            return startInclusive;
        }
        
        return startInclusive + RANDOM.nextInt(endExclusive - startInclusive);
    }
    
    /**
     * 
     * Returns a random long within the specified range.
     * 
     * 
     * @param startInclusive
     *            the smallest value that can be returned, must be non-negative
     * @param endExclusive
     *            the upper bound (not included)
     * @throws IllegalArgumentException
     *             if {@code startInclusive > endExclusive} or if
     *             {@code startInclusive} is negative
     * @return the random long
     */
    public static long nextLong(long startInclusive, long endExclusive) {
        Validate.isTrue(endExclusive >= startInclusive,
                "Start value must be smaller or equal to end value.");
        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");

        if (startInclusive == endExclusive) {
            return startInclusive;
        }

        return (long) nextDouble(startInclusive, endExclusive);
    }    
    
    
    /**
     *  
     * Returns a random double within the specified range.
     * 
     * 
     * @param startInclusive
     *            the smallest value that can be returned, must be non-negative
     * @param endInclusive
     *            the upper bound (included)
     * @throws IllegalArgumentException
     *             if {@code startInclusive > endInclusive} or if
     *             {@code startInclusive} is negative
     * @return the random double
     */
    public static double nextDouble(double startInclusive, double endInclusive) {
        Validate.isTrue(endInclusive >= startInclusive,
                "Start value must be smaller or equal to end value.");
        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
        
        if (startInclusive == endInclusive) {
            return startInclusive;
        }
        
        return startInclusive + ((endInclusive - startInclusive) * RANDOM.nextDouble());
    }
    
    /**
     * 
     * Returns a random float within the specified range.
     * 
     * 
     * @param startInclusive
     *            the smallest value that can be returned, must be non-negative
     * @param endInclusive
     *            the upper bound (included)
     * @throws IllegalArgumentException
     *             if {@code startInclusive > endInclusive} or if
     *             {@code startInclusive} is negative
     * @return the random float
     */
    public static float nextFloat(float startInclusive, float endInclusive) {
        Validate.isTrue(endInclusive >= startInclusive,
                "Start value must be smaller or equal to end value.");
        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
        
        if (startInclusive == endInclusive) {
            return startInclusive;
        }
        
        return startInclusive + ((endInclusive - startInclusive) * RANDOM.nextFloat());
    }    
}