Random random = new Random();
int max = 10;
int min = 3;
int randomNum = random.nextInt(max) % (max - min + 1) + min;

Random random = new Random();
int max = 10;
int min = 3;
int randomNum = random.nextInt(max) % (max - min + 1) + min;

在Java 1.7或更高版本中，执行此操作的标准方法如下：

import java.util.concurrent.ThreadLocalRandom;

// nextInt is normally exclusive of the top value,
// so add 1 to make it inclusive
int randomNum = ThreadLocalRandom.current().nextInt(min, max + 1);

请参阅相关的JavaDoc。这种方法的优点是不需要显式初始化java.util.Random实例，如果使用不当，可能会导致混淆和错误。

然而，相反，没有办法明确设置种子，因此在测试或保存游戏状态等有用的情况下，很难再现结果。在这些情况下，可以使用下面所示的Java 1.7之前的技术。

在Java 1.7之前，执行此操作的标准方法如下：

import java.util.Random;

/**
 * Returns a pseudo-random number between min and max, inclusive.
 * The difference between min and max can be at most
 * <code>Integer.MAX_VALUE - 1</code>.
 *
 * @param min Minimum value
 * @param max Maximum value.  Must be greater than min.
 * @return Integer between min and max, inclusive.
 * @see java.util.Random#nextInt(int)
 */
public static int randInt(int min, int max) {

    // NOTE: This will (intentionally) not run as written so that folks
    // copy-pasting have to think about how to initialize their
    // Random instance.  Initialization of the Random instance is outside
    // the main scope of the question, but some decent options are to have
    // a field that is initialized once and then re-used as needed or to
    // use ThreadLocalRandom (if using at least Java 1.7).
    // 
    // In particular, do NOT do 'Random rand = new Random()' here or you
    // will get not very good / not very random results.
    Random rand;

    // nextInt is normally exclusive of the top value,
    // so add 1 to make it inclusive
    int randomNum = rand.nextInt((max - min) + 1) + min;

    return randomNum;
}

请参阅相关的JavaDoc。实际上，java.util.Random类通常比java.lang.Math.Random（）更好。

特别是，当标准库中有一个简单的API来完成任务时，无需重新发明随机整数生成轮。

Use:

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

只需执行以下语句即可完成：

Randomizer.generate(0, 10); // Minimum of zero and maximum of ten

下面是它的源代码。

文件Randomizer.java

public class Randomizer {
    public static int generate(int min, int max) {
        return min + (int)(Math.random() * ((max - min) + 1));
    }
}

它只是干净和简单。

下面是一个简单的示例，它显示了如何从闭合的[min，max]范围生成随机数，而min<=max为真

您可以将其作为孔中字段类重用，也可以将所有Random.class方法放在一个位置

结果示例：

RandomUtils random = new RandomUtils();
random.nextInt(0, 0); // returns 0
random.nextInt(10, 10); // returns 10
random.nextInt(-10, 10); // returns numbers from -10 to 10 (-10, -9....9, 10)
random.nextInt(10, -10); // throws assert

来源：

import junit.framework.Assert;
import java.util.Random;

public class RandomUtils extends Random {

    /**
     * @param min generated value. Can't be > then max
     * @param max generated value
     * @return values in closed range [min, max].
     */
    public int nextInt(int min, int max) {
        Assert.assertFalse("min can't be > then max; values:[" + min + ", " + max + "]", min > max);
        if (min == max) {
            return max;
        }

        return nextInt(max - min + 1) + min;
    }
}