Java enhanced loop

Question

Please, explain me step by step output of this code:

public class My {
    public static void main(String[] args) {
        int[] a = {1,2,3,4,1};
        for (int n : a) {
            a[n] = 0;
        }
        for (int n : a) {
            System.out.println(n);
        }
    }
}

I know that is an enhanced loop. But do not understand how it works with a[n]=0 Why this code outputs 00301?

It is best to take a piece of paper and do this yourself. For example the first element of the array is 1. The first iteration of the first for loop will set the value of the second element (with index 1) to zero. — Dimitar Spasovski
– Dimitar Spasovski, Commented May 1, 2018 at 10:47
@OP just to point out, the n in this case is iterated through the values stored in a, technically not iterated using a's index — nafas
– nafas, Commented May 1, 2018 at 11:24

jsheeran · Accepted Answer · 2018-05-01 10:47:53Z

3

You can debug this by adding a println statement:

    for (int n : a) {
        System.out.println("Changing element " + n + " of array from " + a[n] + " to 0");
        a[n] = 0;
    }

The output of this is:

Changing element 1 of array from 2 to 0
Changing element 0 of array from 1 to 0
Changing element 3 of array from 4 to 0
Changing element 0 of array from 0 to 0
Changing element 1 of array from 0 to 0

answered May 1, 2018 at 10:47

jsheeran

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1 Comment

Дмитрий Б Over a year ago

Thank you so much!

Sanjeev Guglani · Accepted Answer · 2018-05-01 10:53:17Z

0

This code is actually replacing value of nth index where n is the value assign to n while traversing

answered May 1, 2018 at 10:53

Sanjeev Guglani

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Comments

Sameersharma9 · Accepted Answer · 2018-05-02 04:51:57Z

0

While iterating over the array a[], it changes the value of array. This is why a[2] and a[4] is never changed.

answered May 2, 2018 at 4:51

Sameersharma9

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