org.apache.commons.lang.math.JVMRandom Maven / Gradle / Ivy
/*
* 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.lang.math;
import java.util.Random;
/**
* JVMRandom is a wrapper that supports all possible
* Random methods via the {@link java.lang.Math#random()} method
* and its system-wide {@link Random} object.
*
* It does this to allow for a Random class in which the seed is
* shared between all members of the class - a better name would
* have been SharedSeedRandom.
*
* N.B. the current implementation overrides the methods
* {@link Random#nextInt(int)} and {@link Random#nextLong()}
* to produce positive numbers ranging from 0 (inclusive)
* to MAX_VALUE (exclusive).
*
* @since 2.0
* @version $Id: JVMRandom.java 911986 2010-02-19 21:19:05Z niallp $
*/
public final class JVMRandom extends Random {
/**
* Required for serialization support.
*
* @see java.io.Serializable
*/
private static final long serialVersionUID = 1L;
private static final Random SHARED_RANDOM = new Random();
/**
* Ensures that only the parent constructor can call reseed.
*/
private boolean constructed = false;
/**
* Constructs a new instance.
*/
public JVMRandom() {
this.constructed = true;
}
/**
* Unsupported in 2.0.
*
* @param seed ignored
* @throws UnsupportedOperationException
*/
public synchronized void setSeed(long seed) {
if (this.constructed) {
throw new UnsupportedOperationException();
}
}
/**
* Unsupported in 2.0.
*
* @return Nothing, this method always throws an UnsupportedOperationException.
* @throws UnsupportedOperationException
*/
public synchronized double nextGaussian() {
throw new UnsupportedOperationException();
}
/**
* Unsupported in 2.0.
*
* @param byteArray ignored
* @throws UnsupportedOperationException
*/
public void nextBytes(byte[] byteArray) {
throw new UnsupportedOperationException();
}
/**
*
Returns the next pseudorandom, uniformly distributed int value
* from the Math.random() sequence.
* Identical to nextInt(Integer.MAX_VALUE)
*
* N.B. All values are >= 0.
*
* @return the random int
*/
public int nextInt() {
return nextInt(Integer.MAX_VALUE);
}
/**
* Returns a pseudorandom, uniformly distributed int value between
* 0 (inclusive) and the specified value (exclusive), from
* the Math.random() sequence.
*
* @param n the specified exclusive max-value
* @return the random int
* @throws IllegalArgumentException when n <= 0
*/
public int nextInt(int n) {
return SHARED_RANDOM.nextInt(n);
}
/**
* Returns the next pseudorandom, uniformly distributed long value
* from the Math.random() sequence.
* Identical to nextLong(Long.MAX_VALUE)
*
* N.B. All values are >= 0.
*
* @return the random long
*/
public long nextLong() {
return nextLong(Long.MAX_VALUE);
}
/**
* Returns a pseudorandom, uniformly distributed long value between
* 0 (inclusive) and the specified value (exclusive), from
* the Math.random() sequence.
*
* @param n the specified exclusive max-value
* @return the random long
* @throws IllegalArgumentException when n <= 0
*/
public static long nextLong(long n) {
if (n <= 0) {
throw new IllegalArgumentException(
"Upper bound for nextInt must be positive"
);
}
// Code adapted from Harmony Random#nextInt(int)
if ((n & -n) == n) { // n is power of 2
// dropping lower order bits improves behaviour for low values of n
return next63bits() >> 63 // drop all the bits
- bitsRequired(n-1); // except the ones we need
}
// Not a power of two
long val;
long bits;
do { // reject some values to improve distribution
bits = next63bits();
val = bits % n;
} while (bits - val + (n - 1) < 0);
return val;
}
/**
* Returns the next pseudorandom, uniformly distributed boolean value
* from the Math.random() sequence.
*
* @return the random boolean
*/
public boolean nextBoolean() {
return SHARED_RANDOM.nextBoolean();
}
/**
* Returns the next pseudorandom, uniformly distributed float value
* between 0.0 and 1.0 from the Math.random()
* sequence.
*
* @return the random float
*/
public float nextFloat() {
return SHARED_RANDOM.nextFloat();
}
/**
* Synonymous to the Math.random() call.
*
* @return the random double
*/
public double nextDouble() {
return SHARED_RANDOM.nextDouble();
}
/**
* Get the next unsigned random long
* @return unsigned random long
*/
private static long next63bits(){
// drop the sign bit to leave 63 random bits
return SHARED_RANDOM.nextLong() & 0x7fffffffffffffffL;
}
/**
* Count the number of bits required to represent a long number.
*
* @param num long number
* @return number of bits required
*/
private static int bitsRequired(long num){
// Derived from Hacker's Delight, Figure 5-9
long y=num; // for checking right bits
int n=0; // number of leading zeros found
while(true){
// 64 = number of bits in a long
if (num < 0) {
return 64-n; // no leading zeroes left
}
if (y == 0) {
return n; // no bits left to check
}
n++;
num=num << 1; // check leading bits
y=y >> 1; // check trailing bits
}
}
}