First, Last and Reversed (Sequenced Collections, Java 21)

/*
 * Problem : Process an array.
 * Input   : n, then n integers.
 * Output  : Three lines.
 * Approach: Index arithmetic and a copy.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(int[] a) {
        // Step 1: Put the numbers in a list.
        java.util.List<Integer> list = new java.util.ArrayList<>();
        for (int value : a) {
            list.add(value);
        }

        // Step 2: Before Java 21 the first and last elements need index arithmetic.
        int first = list.get(0);
        int last = list.get(list.size() - 1);

        // Step 3: To get the reversed order we must copy the list and call Collections.reverse.
        java.util.List<Integer> copy = new java.util.ArrayList<>(list);
        java.util.Collections.reverse(copy);

        StringBuilder text = new StringBuilder();
        for (int value : copy) {
            text.append(text.length() == 0 ? "" : " ").append(value);
        }
        return new String[] {"first: " + first, "last: " + last, "reversed: " + text};
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(String.join("\n", solve(a)));
    }
}