Reverse a List in Java

Question

Why this code for reverse a list in java doesn't work correctly?

import java.util.List;
public class Main{
public static List<Integer> reverseArray(List<Integer> a){
        int n = a.size();
        int temp = 0;
        for (int i = 0; i < n/2; i++){
            temp = a.get(n-1);
            a.set(n-1, a.get(i));
            a.set(i, temp);
            n--;
        }
        return a;
    }
}

Answer 1

I wouldn't use such an implementation as you're being destructive to the parameter. If you're going to return a list, then create a new list. Anyone using such a function will assume their source list will remain unaltered, but with your implementation, that isn't true. Do something more like this:

public static <T> List<T> reverse(List<T> list) {
    List<T> reverse = new ArrayList<>();

    for (int i = list.size() - 1; i >= 0; i--) {
        reverse.add(list.get(i));
    }

    return reverse;
}