负数不会进入int

Question

我在java中有以下代码.在这里,我试图看到一个数组的随机组合.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Random;

public class Dummy {
    public static void main(String args[]) throws Exception {
        Random rand = new Random();

        int[] a = { 1, 2, 3, 4, 5 };
        int[] b = { 1, 0, 1, 0, 1 };
        Arrays.sort(a);
        Arrays.sort(b);
        int x = a.length * b.length;
        System.out.println(x);

        ArrayList<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < 25; i++) {

            System.out.println("random of i is" + a[rand.nextInt(i)]
                    + "and j is " + b[rand.nextInt(i)]);

        }
        System.out.println(list);

    }
}

在这里我得到以下错误.

Exception in thread "main" java.lang.IllegalArgumentException: n must be positive
    at java.util.Random.nextInt(Unknown Source)
    at Dummy.main(Dummy.java:20)

请让我知道如何解决它.根据基于相似问题的其他一些帖子,我发现只有正数才会给出随机数,我想知道我怎样才能给出负数.

此外,我想知道通过延续[]和b []可以获得多少组合.

谢谢

Answer 1

你error是因为你传球0 rand.nextInt(i).

rand.nextInt() expects positive integer greater that 0.