ArrayIndexOutOfBoundsException - Quicksort Algorithm

Question

So this is my code. The error is ArrayIndexOutOfBoundsException, below I have mentioned it. Please help me find the cause.

import java.util.Scanner;

public class sort {

    public static void main(String args[]){
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the number of entries");
        int[] arr = new int[s.nextInt()];
        System.out.println("Enter the numbers");
        for(int i=0;i<arr.length;i++)
            arr[i] = s.nextInt();
        s.close();
        QuickSort.sort(arr);
        for(int i=0;i<arr.length;i++)
            System.out.print(arr[i]+" ");
    }
}

public class QuickSort {

    private static int partition(int[] arr, int hi, int lo){
        int i=lo,j=hi+1,swap=0;
        while(true){
            while(arr[++i]<arr[lo])
                if(i==hi)break;
            while(arr[--j]>arr[lo]) \\error line
                if(j==lo)break;
            if(j<=i)break;
            swap=arr[i];
            arr[i]=arr[j];
            arr[j]=swap;
        }
        swap=arr[lo];
        arr[lo]=arr[j];
        arr[j]=swap;
        return j;   
    }
    public static void sort(int[] arr){
        sort(arr,arr.length-1,0);
    }
    private static void sort(int[] arr,int hi,int lo){
        int j = partition(arr,hi,lo);
        sort(arr,j-1,lo);
        sort(arr,hi,j+1);
    }

}

Error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at riku.QuickSort.partition(QuickSort.java:10) at riku.QuickSort.sort(QuickSort.java:28) at riku.QuickSort.sort(QuickSort.java:29) at riku.QuickSort.sort(QuickSort.java:29) at riku.QuickSort.sort(QuickSort.java:29) at riku.QuickSort.sort(QuickSort.java:25) at riku.sort.main(sort.java:12) this is the complete error log

Answer 1

j getting to 0, then arr[--j] is evaluating to arr[-1] you have to make sure that index never gets below zero.

Another approach would be to use recursion, it would be much simpler but can cause stack overflow for large arrays.