001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3;
018
019import java.util.Random;
020
021/**
022 * <p>Utility library that supplements the standard {@link Random} class.</p>
023 * 
024 * @since 3.3
025 *
026 * @version $Id: RandomUtils.java 1580464 2014-03-23 07:28:42Z djones $
027 */
028public class RandomUtils {
029
030    /**
031     * Random object used by random method. This has to be not local to the
032     * random method so as to not return the same value in the same millisecond.
033     */
034    private static final Random RANDOM = new Random();
035
036    /**
037     * <p>
038     * {@code RandomUtils} instances should NOT be constructed in standard
039     * programming. Instead, the class should be used as
040     * {@code RandomUtils.nextBytes(5);}.
041     * </p>
042     * 
043     * <p>
044     * This constructor is public to permit tools that require a JavaBean
045     * instance to operate.
046     * </p>
047     */
048    public RandomUtils() {
049        super();
050    }
051
052    /**
053     * <p>
054     * Creates an array of random bytes.
055     * </p>
056     * 
057     * @param count
058     *            the size of the returned array
059     * @return the random byte array
060     * @throws IllegalArgumentException if {@code count} is negative
061     */
062    public static byte[] nextBytes(int count) {
063        Validate.isTrue(count >= 0, "Count cannot be negative.");
064
065        byte[] result = new byte[count];
066        RANDOM.nextBytes(result);
067        return result;
068    }
069
070    /**
071     * <p>
072     * Returns a random integer within the specified range.
073     * </p>
074     * 
075     * @param startInclusive
076     *            the smallest value that can be returned, must be non-negative
077     * @param endExclusive
078     *            the upper bound (not included)
079     * @throws IllegalArgumentException
080     *             if {@code startInclusive > endExclusive} or if
081     *             {@code startInclusive} is negative
082     * @return the random integer
083     */
084    public static int nextInt(int startInclusive, int endExclusive) {
085        Validate.isTrue(endExclusive >= startInclusive,
086                "Start value must be smaller or equal to end value.");
087        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
088
089        if (startInclusive == endExclusive) {
090            return startInclusive;
091        }
092        
093        return startInclusive + RANDOM.nextInt(endExclusive - startInclusive);
094    }
095    
096    /**
097     * <p>
098     * Returns a random long within the specified range.
099     * </p>
100     * 
101     * @param startInclusive
102     *            the smallest value that can be returned, must be non-negative
103     * @param endExclusive
104     *            the upper bound (not included)
105     * @throws IllegalArgumentException
106     *             if {@code startInclusive > endExclusive} or if
107     *             {@code startInclusive} is negative
108     * @return the random long
109     */
110    public static long nextLong(long startInclusive, long endExclusive) {
111        Validate.isTrue(endExclusive >= startInclusive,
112                "Start value must be smaller or equal to end value.");
113        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
114
115        if (startInclusive == endExclusive) {
116            return startInclusive;
117        }
118
119        return (long) nextDouble(startInclusive, endExclusive);
120    }    
121    
122    
123    /**
124     * <p> 
125     * Returns a random double within the specified range.
126     * </p>
127     * 
128     * @param startInclusive
129     *            the smallest value that can be returned, must be non-negative
130     * @param endInclusive
131     *            the upper bound (included)
132     * @throws IllegalArgumentException
133     *             if {@code startInclusive > endInclusive} or if
134     *             {@code startInclusive} is negative
135     * @return the random double
136     */
137    public static double nextDouble(double startInclusive, double endInclusive) {
138        Validate.isTrue(endInclusive >= startInclusive,
139                "Start value must be smaller or equal to end value.");
140        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
141        
142        if (startInclusive == endInclusive) {
143            return startInclusive;
144        }
145        
146        return startInclusive + ((endInclusive - startInclusive) * RANDOM.nextDouble());
147    }
148    
149    /**
150     * <p>
151     * Returns a random float within the specified range.
152     * </p>
153     * 
154     * @param startInclusive
155     *            the smallest value that can be returned, must be non-negative
156     * @param endInclusive
157     *            the upper bound (included)
158     * @throws IllegalArgumentException
159     *             if {@code startInclusive > endInclusive} or if
160     *             {@code startInclusive} is negative
161     * @return the random float
162     */
163    public static float nextFloat(float startInclusive, float endInclusive) {
164        Validate.isTrue(endInclusive >= startInclusive,
165                "Start value must be smaller or equal to end value.");
166        Validate.isTrue(startInclusive >= 0, "Both range values must be non-negative.");
167        
168        if (startInclusive == endInclusive) {
169            return startInclusive;
170        }
171        
172        return startInclusive + ((endInclusive - startInclusive) * RANDOM.nextFloat());
173    }    
174}