使用 arraylist 而不是数组

Question

The code is designed for the array, I want to use ArrayList in this code, the code ArrayList is added below the origin array. But the code seems like can't read the elements in the ArrayList. How can I make it possible?

It only returns 0 now, and I guess that's because it can't read the elements in the ArrayList?

Here is my code. Why did this happen and how can I fix it?

import java.util.*; 
class RandomisedQuickSort 
{ 
    public static int N = 5; 
    public static int[] arr = new int[N]; 
    
    void random(int low,int high) 
    { 
    
        Random rand= new Random(); 
        int pivot = rand.nextInt(high-low) + low; 
        
        int temp1=arr[pivot]; 
        arr[pivot]=arr[high]; 
        arr[high]=temp1; 
    } 
    
    int partition(int arr[], int low, int high) 
    { 
        int pivot = arr[high]; 
    

        int i = (low-1);
        for (int j = low; j < high; j++) 
        { 
        
            if (arr[j] <= pivot) 
            { 
                i++; 

                int temp = arr[i]; 
                arr[i] = arr[j]; 
                arr[j] = temp; 
            } 
        } 

        int temp = arr[i+1]; 
        arr[i+1] = arr[high]; 
        arr[high] = temp; 

        return i+1; 
    } 

    void sort(int arr[], int low, int high) 
    { 
        if (low < high) 
        { 
            int pi = partition(arr, low, high); 

            sort(arr, low, pi-1); 
            sort(arr, pi+1, high); 
        } 
    } 

    static void printArray(int arr[]) 
    { 
        int n = arr.length; 
        for (int i = 0; i < n; ++i) 
            System.out.print(arr[i]+" "); 
        System.out.println(); 
    } 

    public static void main(String args[]) 
    { 
        //int arr[] = {10, 7, 8, 9, 1, 5}; 

        ArrayList<Integer> list = new ArrayList<>();
        
        for (int i = 1; i <= 10; i++) {
            list.add(i);
        }
        Collections.shuffle(list);
                    
        int n = arr.length; 
        
        RandomisedQuickSort ob = new RandomisedQuickSort(); 
        ob.sort(arr, 0, n-1); 

        System.out.println("sorted array"); 
        printArray(arr); 
    } 
}

Answer 1

You are using Integer[] but sort() and printArray() expect int[]

void sort(int arr[], int low, int high) {...}
static void printArray(int arr[]) {..}

You can convert Arraylist into int[] this way and use

 int[] arr = list.stream().mapToInt(i->i).toArray();