Thread: Problems with replacing indexs in an array

it somewhat works only when i use 8as my first index insted of 9

Can you post the different results that show what you are talking about? Add some comments to the output describing the problem and show the desired output.

if i use 8 inside the second loop fo i
[16, 6, 9, 8, 4, 5, 8, 16, 15, 14, 18, 6, 12, 18, 19, 13, 7, 19, 13, 1]
[18, 6, 12, 18, 19, 13, 7, 19, 13, 1, 16, 15, 16, 6, 9, 8, 4, 5, 8, 14]
it somewhat works,until it reaches the middle and than gets all wonky,
on second try-
[9, 1, 12, 5, 20, 17, 16, 12, 15, 9, 9, 14, 19, 1, 6, 2, 5, 4, 20, 5]
[9, 14, 19, 1, 6, 2, 5, 4, 20, 5, 12, 15, 9, 1, 12, 5, 20, 17, 16, 9]
Still...works a bit wonky but works halfway.
If i use 10 for the index in the second loop,(which logicaly thinking sounds right to me)
[2, 3, 2, 6, 20, 2, 19, 17, 20, 13, 3, 2, 10, 13, 15, 2, 17, 19, 6, 12]
[10, 13, 15, 2, 17, 19, 6, 12, 13, 3, 2, 3, 2, 6, 20, 2, 19, 17, 20, 2]
it starts the swap from the 13 number insted of the 10th

The way i want it to be is
[16, 6, 9, 8, 4, 5, 8, 16, 15, 14, 18, 6, 12, 18, 19, 13, 7, 19, 13, 1]
[18, 6, 12, 18, 19, 13, 7, 19, 13, 1,16, 6, 9, 8, 4, 5, 8, 16, 15, 14]

Edit**
ive changed the second loop and got it working,but i still fail to see why it didnt work before,
heres the new loop

package page48;
 
import java.util.Arrays;
import java.util.Random;
 
public class Drill4 {
 
	public static void main(String[] args) {
 
		int[] array = new int[20];
		Random rand = new Random();
		int j = 0;
		int temp = 0;
 
		for (int i = 0; i < array.length; i++) {
			array[i] = rand.nextInt(20) + 1;
 
		}
		System.out.println(Arrays.toString(array));
		for (int i = 10; i < array.length; i++) {
			temp = array[i];
			array[i] = array[j];
			array[j] = temp;
			j++;
 
		}
		System.out.println(Arrays.toString(array));
 
	}
}

What does the value of 8 represent? Why was that value chosen as a loop start point?

replace the first index with the 10th and so on,

I don't understand what those instructions say. Can you show an example on an array with numbers in order:
Given this input: [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
what is the desired output?

Using random values for testing makes it hard to see if the code is making the desired result.

why it didnt work before

Because the logic was wrong.
There was no need for a nested loop.
The program is simply swapping elements from index starting at 0 (in j) with those from index starting at 10 (in i)