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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.
/*
* 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.
*
* Caveat: Instances of {@link Random} are not cryptographically secure.
*
* Please note that the Apache Commons project provides a component
* dedicated to pseudo-random number generation, namely
* Commons RNG, that may be
* a better choice for applications with more stringent requirements
* (performance and/or correctness).
*
* @since 3.3
*/
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() {
}
/**
*
* Returns a random boolean value
*
*
* @return the random boolean
* @since 3.5
*/
public static boolean nextBoolean() {
return RANDOM.nextBoolean();
}
/**
*
* 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(final int count) {
Validate.isTrue(count >= 0, "Count cannot be negative.");
final 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(final int startInclusive, final 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 int within 0 - Integer.MAX_VALUE
*
* @return the random integer
* @see #nextInt(int, int)
* @since 3.5
*/
public static int nextInt() {
return nextInt(0, Integer.MAX_VALUE);
}
/**
*
* 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(final long startInclusive, final 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 startInclusive + nextLong(endExclusive - startInclusive);
}
/**
* Returns a random long within 0 - Long.MAX_VALUE
*
* @return the random long
* @see #nextLong(long, long)
* @since 3.5
*/
public static long nextLong() {
return nextLong(Long.MAX_VALUE);
}
/**
* Generates a {@code long} value between 0 (inclusive) and the specified
* value (exclusive).
*
* @param n Bound on the random number to be returned. Must be positive.
* @return a random {@code long} value between 0 (inclusive) and {@code n}
* (exclusive).
*/
private static long nextLong(final long n) {
// Extracted from o.a.c.rng.core.BaseProvider.nextLong(long)
long bits;
long val;
do {
bits = RANDOM.nextLong() >>> 1;
val = bits % n;
} while (bits - val + (n - 1) < 0);
return val;
}
/**
*
* Returns a random double 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 double
*/
public static double nextDouble(final double startInclusive, final double 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 + ((endExclusive - startInclusive) * RANDOM.nextDouble());
}
/**
* Returns a random double within 0 - Double.MAX_VALUE
*
* @return the random double
* @see #nextDouble(double, double)
* @since 3.5
*/
public static double nextDouble() {
return nextDouble(0, Double.MAX_VALUE);
}
/**
*
* Returns a random float 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 float
*/
public static float nextFloat(final float startInclusive, final float 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 + ((endExclusive - startInclusive) * RANDOM.nextFloat());
}
/**
* Returns a random float within 0 - Float.MAX_VALUE
*
* @return the random float
* @see #nextFloat(float, float)
* @since 3.5
*/
public static float nextFloat() {
return nextFloat(0, Float.MAX_VALUE);
}
}