java - ArrayIndexOutOfBoundsException : -1 in recursive sorting

Question

我是 Java 新手，我想知道为什么我有异常，即使我得到了我需要的答案。下面是源代码

package habeeb;

import java.util.*;

public class Habeeb
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int[] num = new int[30];
        int i, count = 0;
        System.out.println("Enter the integers between 1 and 100");
        for (i = 1; i <= num.length; i++)
        {
            num[i] = input.nextInt();
            if (num[i] == 0)
                break;
            count++;
        }
        Sorting(num, i, count);
    }

    public static void Sorting(int[] sort, int a, int con)
    {
        int j, count = 0;
        for (j = 1; j <= con; j++)
        {
            if (sort[a] == sort[j])
                count++;
        }
        System.out.println(sort[a] + " occurs " + count + " times");
        Sorting(sort, a - 1, con);
    }
}

这是输出

run:
Enter the integers between 1 and 100
1
2
3
2
2
4
5
3
6
1
0
0 occurs 0 times
1 occurs 2 times
6 occurs 1 times
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
3 occurs 2 times
5 occurs 1 times
4 occurs 1 times
2 occurs 3 times
2 occurs 3 times
3 occurs 2 times
2 occurs 3 times
1 occurs 2 times
0 occurs 0 times
 at habeeb.Habeeb.Sorting(Habeeb.java:18)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.Sorting(Habeeb.java:21)
 at habeeb.Habeeb.main(Habeeb.java:14)
 Java Result: 1

Answer 1

public static void Sorting(int[] sort, int a, int con){
int j, count=0;
for(j=1; j<=con; j++){
  if(sort[a]==sort[j])
   count++;
}System.out.println(sort[a]+" occurs "+count+" times"); 
Sorting(sort, a-1, con);

应该是:

public static void Sorting(int[] sort, int a, int con){
if(a<0)return;
int j, count=0;
for(j=1; j<=con; j++){
  if(sort[a]==sort[j])
   count++;
}System.out.println(sort[a]+" occurs "+count+" times"); 
Sorting(sort, a-1, con);