如何在特定范围内生成随机int值？
以下方法存在与整数溢出相关的错误：
randomNum = minimum + (int)(Math.random() * maximum);
// Bug: `randomNum` can be bigger than `maximum`.
Random rn = new Random();
int n = maximum - minimum + 1;
int i = rn.nextInt() % n;
randomNum = minimum + i;
// Bug: `randomNum` can be smaller than `minimum`.
当前回答
我正在考虑使用以下方法将生成的随机数线性归一化到所需范围。设x为随机数，设a和b为期望归一化数的最小和最大范围。
下面是一个非常简单的代码片段，用来测试线性映射产生的范围。
public static void main(String[] args) {
int a = 100;
int b = 1000;
int lowest = b;
int highest = a;
int count = 100000;
Random random = new Random();
for (int i = 0; i < count; i++) {
int nextNumber = (int) ((Math.abs(random.nextDouble()) * (b - a))) + a;
if (nextNumber < a || nextNumber > b) {
System.err.println("number not in range :" + nextNumber);
}
else {
System.out.println(nextNumber);
}
if (nextNumber < lowest) {
lowest = nextNumber;
}
if (nextNumber > highest) {
highest = nextNumber;
}
}
System.out.println("Produced " + count + " numbers from " + lowest
+ " to " + highest);
}
其他回答
范围[最小值最大值]（含）内的随机数：
int randomFromMinToMaxInclusive = ThreadLocalRandom.current()
.nextInt(min, max + 1);
Use:
Random ran = new Random();
int x = ran.nextInt(6) + 5;
整数x现在是可能结果为5-10的随机数。
Use:
minValue + rn.nextInt(maxValue - minValue + 1)
使用这些方法可能很方便：
此方法将返回提供的最小值和最大值之间的随机数：
public static int getRandomNumberBetween(int min, int max) {
Random foo = new Random();
int randomNumber = foo.nextInt(max - min) + min;
if (randomNumber == min) {
// Since the random number is between the min and max values, simply add 1
return min + 1;
} else {
return randomNumber;
}
}
并且该方法将从所提供的最小值和最大值返回随机数（因此生成的数也可以是最小值或最大值）：
public static int getRandomNumberFrom(int min, int max) {
Random foo = new Random();
int randomNumber = foo.nextInt((max + 1) - min) + min;
return randomNumber;
}
import java.util.Random;
public class RandomUtil {
// Declare as class variable so that it is not re-seeded every call
private static Random random = new Random();
/**
* Returns a psuedo-random number between min and max (both inclusive)
* @param min Minimim value
* @param max Maximim value. Must be greater than min.
* @return Integer between min and max (both inclusive)
* @see java.util.Random#nextInt(int)
*/
public static int nextInt(int min, int max) {
// nextInt is normally exclusive of the top value,
// so add 1 to make it inclusive
return random.nextInt((max - min) + 1) + min;
}
}
