Reverse an array, but doesn't work

Question

I know this is pretty basic, but I don't know why my code doesn't work. The code below is supposed to reverse the array, but I'm seriously dying to know why the output stays the same! Any explanation will be appreciated :)

public class Test {
    public static void main(String[] args) {
        int[] oldList = {1, 2, 3, 4, 5};
        reverse(oldList);
        for (int i = 0; i < oldList.length; i++)
            System.out.print(oldList[i] + " ");
    }
    public static void reverse(int[] list) {
        int[] newList = new int[list.length];
        for (int i = 0; i < list.length; i++)
            newList[newList.length] = list[list.length - 1 - i];
        list = newList;
    }
}

`list = newList` does not change the array in your `main` method. — Jorn Vernee, Dec 13 '16 at 00:11

score 1 · Accepted Answer · answered Dec 13 '16 at 00:13

1

You will have to modify the method according to the following:

public class Test {
    public static void main(String[] args) {
        int[] oldList = {1, 2, 3, 4, 5};
        oldList = reverse(oldList); //assign the returned value from the method
        for (int i = 0; i < oldList.length; i++)
            System.out.print(oldList[i] + " ");
    }
    public static int[] reverse(int[] list) {
        int[] newList = new int[list.length];
        for (int i = 0; i < list.length; i++)
            newList[newList.length] = list[list.length - 1 - i];
        list = newList;
        return list;
    }
}

To find more details about this read more about pass by value and pass by reference in Java.

answered Dec 13 '16 at 00:13

Pritam Banerjee

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Can you explain why omitting void solve the problem? What's the problem with void? I thought the list array is static, so it should work? – Jordan Dec 13 '16 at 00:23
@PemiNg `void` in front of a method means it won't return anything. But you will have to return the `int[]`. – Pritam Banerjee Dec 13 '16 at 00:25
Thanks! now I get it! – Jordan Dec 13 '16 at 00:40
@PemiNg If it helped can you please accept the answer? – Pritam Banerjee Dec 13 '16 at 00:41
1

Already did! Thanks a lot – Jordan Dec 15 '16 at 19:15

Reverse an array, but doesn't work

1 Answers1