System.currentTimeMillis()

通过System.currentTimeMillis()来获取随机数，实际上是获取当前时间毫秒数，它是long类型

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/**
 * @author LeDao
 * @company
 * @create 2021-06-21 12:38
 */
public class Test {

    public static void main(String[] args) {
        long l = System.currentTimeMillis();
        System.out.println(l);
    }
}

Math.random()

它返回的是0(包含)到1(不包含)之间的double值，如果要返回[0,100]的int整数，只需要将获得的结果乘以100再转换为int类型即可

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/**
 * @author LeDao
 * @company
 * @create 2021-06-21 12:38
 */
public class Test {

    public static void main(String[] args) {
        //[0,1)
        double d = Math.random();
        System.out.println(d);
        //[0,100]
        int i = (int) (d * 100);
        System.out.println(i);
    }
}

Random.nextInt(int bound)

获取[0,bound-1]的int整数

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import java.util.Random;

/**
 * @author LeDao
 * @company
 * @create 2021-06-21 12:38
 */
public class Test {

    public static void main(String[] args) {
        Random random = new Random();
        //[0,99]
        int i = random.nextInt(100);
        System.out.println(i);
    }
}