如果可以交换的话, 那么可以这么写:

import java.util.* ;

public class Main
{
    public static void shuffle(int[] arr)
    {
        Random rand = new Random(System.currentTimeMillis()) ;
        for(int i=0 ; i<arr.length ; i++)
        {
            int pos = i + rand.nextInt(arr.length-i) ;
            swap(arr , i , pos) ;
        }
    }
    
    public static void swap(int[] arr , int i , int j)
    {
        int x = arr[i] ;
        arr[i] = arr[j] ;
        arr[j] = x ;
    }
    
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in) ;
        int n = sc.nextInt() ;
        int[] arr = new int[n] ;
        for(int i=0 ; i<n ; i++)
        {
            arr[i] = i ;
        }
        Main.shuffle(arr) ;
        System.out.println(Arrays.toString(arr)) ;
    }
}

但是题主题目明确说不能更换, 我没办法啦╮(╯▽╰)╭

后来我试着这样也能！因为你的帮助有了想法
public static void main(String args[]) 
{ 
final int n = 8; 
int[] numbers = new int[n]; 

// builds 
for (int i = 0; i < numbers.length; i++) { 
numbers[i] = i + 1; 
} 

// generates 
for (int i = 0; i < numbers.length; i++) { 
int pos = new Random().nextInt(n); 
int temp = numbers[i]; 
numbers[i] = numbers[pos]; 
numbers[pos] = temp; 
} 

System.out.println(Arrays.toString(numbers)); 
}

or

import java.util.Scanner; 
import java.util.Random; 
public class perm { 
public static void main(String[] arg){ 
Scanner s = new Scanner(System.in); 
int N = s.nextInt(),i; 
int[] seq = new int[N]; 
for(i=N-1;i>=0;--i)seq[i]=1+i; 
for(i=0;i<N;++i) System.out.printf(" "+seq[i]); 
System.out.printf("\n random permutation \n"); 
Random rg = new Random(); 
for(i=N*N*N;0<i;--i) { 
int n0 = rg.nextInt(N); 
int n1 = rg.nextInt(N); 
if(n0 != n1) { 
int t = seq[n0]; 
seq[n0] = seq[n1]; 
seq[n1] = t; 
} 
} 
for(i=0;i<N;++i) System.out.printf(" "+seq[i]); 
System.out.printf("\n"); 
System.exit(0); 
} 
}