每当我在 java 中运行插入排序程序时，都会发生异常.. 但我不知道为什么

Question

Below is my code for Insertion Sort and i am facing an exception of array indexing.

import java.util.Scanner;

public class Insertion_Sort {

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=4;
        int ar[]=new int[n];
        for(int i=0;i<n;i++)
        {
            ar[i]=sc.nextInt();
        }
        for(int i=1;i<n;i++)
        {
            int c=ar[i];
            int j=i-1;
            while(ar[j]>ar[j+1] && j>=0)
            {
                ar[j+1]=ar[j];
                j--;
            }
            ar[j+1]=c;
            
        }
        for(int i=0;i<n;i++)
        {
            System.out.println(ar[i]);
        }
        

    }

}

This is the exception i am getting everytime i run this

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index -1 out of bounds for length 4
    at dfsd.Insertion_Sort.main(Insertion_Sort.java:17)

Answer 1

First thing is that you should check j >= 0 first and if that happen check second condition which is ar[j] > ar[i] . but there is another problem ar array is changing during the process and you should use c instead of ar[i] so the condition would be: j >= 0 && ar[j] > c . Here is the working version of your code:

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = 4;
    int ar[] = new int[n];
    for (int i = 0; i < n; i++) {
        ar[i] = sc.nextInt();
    }
    for (int i = 1; i < n; i++) {
        int c = ar[i];
        int j = i - 1;
        while (j >= 0 && ar[j] > c) {
            ar[j + 1] = ar[j];
            j--;
        }
        ar[j + 1] = c;

    }
    for (int i = 0; i < n; i++) {
        System.out.println(ar[i]);
    }

}

Answer 2

J>=0 should be the first condition. Also you need to check j<n as you are using j+1 in the check (scenario when i reached n-1) to avoid exceptions. The logic of insertion sort seems to be incorrect.