Question

Why does think not work? It just prints zeros. However it works when I use a normal for loop with an index value ‘i’ and using ‘a[i]’ inside the body of the loop.

The problem is not with the printing loop, as it does not print the values, even with a normal for loop.

import java.util.Scanner;

public class Main {

public static void main(String[] args) {

    Scanner s = new Scanner(System.in);
    int[] a = new int[5];
    for (int i : a)
    {
        System.out.println("Enter number : ");
        i=s.nextInt();

    }
    System.out.println("\nThe numbers you entered are : \n");
    for (int i : a)
    {
        System.out.println(i);
    }
}
}

Answer 1

When you access the element using enhanced for-loop: –

for (int i : a)
{
    System.out.println("Enter number : ");
    i=s.nextInt();

}

Here, int i is a copy of element in the array. When you modify it, the change will not get reflected in the array. That’s why the array elements are 0.

So, you need to iterate using traditional for-loop and access the array elements on that index to assign values to it.

Even if your array was an array of some reference, it would still not work. That’s because, the variable in a for-each is not a proxy for an array or Collection reference. For-each assigns each entry in the array to the variable in the loop.

So, your enhanced for-loop: –

for (Integer i: arr) {
    i = new Integer();
}

is converted to: –

for (int i = 0; i < arr.length; i++) {
    Integer i = arr[i];
    i = new Integer();
}

So, the initialization of i in the loop, is not reflected in the array. And thus the array elements are null.

Workarond: –

1. use traditional for loop: –

   for (int i = 0; i < a.length; i++) {
       a[i] = sc.nextInt();
   }