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

Use:

minValue + rn.nextInt(maxValue - minValue + 1)

其他回答

Random rng = new Random();
int min = 3;
int max = 11;
int upperBound = max - min + 1; // upper bound is exclusive, so +1
int num = min + rng.nextInt(upperBound);
System.out.println(num);

Java 17引入了RandomGenerator接口,它提供了一个int nextInt(int origin,int bound)方法来获取范围内的随机整数:

// Returns a random int between minimum (inclusive) & maximum (exclusive)
int randomInt = RandomGenerator.getDefault().nextInt(minimum, maximum);

除了用于Java17中添加的新的随机生成算法之外,该接口还添加到现有的随机生成类(random、SecureRandom、SplitableRandom和ThreadLocalRandom)中。因此,从Java 17开始,这些类具有以下有界nextInt方法:

new Random().nextInt(minimum, maximum);
new SecureRandom().nextInt(minimum, maximum);
new SplittableRandom().nextInt(minimum, maximum);
new ThreadLocalRandom().nextInt(minimum, maximum);

从Java17开始,这种方法是Random和SecureRandom的新方法。在Java17之前,ThreadLocalRandom和SplitableRandom已经有了这个方法,尽管它不是由共享接口指定的。

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;
}
private static Random random = new Random();    

public static int getRandomInt(int min, int max){
  return random.nextInt(max - min + 1) + min;
}

OR

public static int getRandomInt(Random random, int min, int max)
{
  return random.nextInt(max - min + 1) + min;
}

使用Java 8 Streams,

传递初始容量-多少个数字将randomBound从x传递到randomBoud是否为已排序传递true/false传递新的Random()对象

 

public static List<Integer> generateNumbers(int initialCapacity, int randomBound, Boolean sorted, Random random) {

    List<Integer> numbers = random.ints(initialCapacity, 1, randomBound).boxed().collect(Collectors.toList());

    if (sorted)
        numbers.sort(null);

    return numbers;
}

在本例中,它从1-Randombound生成数字。