定义一个长度为n的数组，将数组的第一个元素与第n个元素交换位置，第二个与第n-1个元素交换位置，……，输出交换之后的数组

运行效果如下

import java.util.Scanner;

public class A {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("请输入n:");
    int n = sc.nextInt();
    int a[] = new int[n];
    System.out.println("请输入n个元素：");
    for (int i = 0; i < n; i++) {
      a[i] = sc.nextInt();
    }
    sc.close();
    System.out.println("交换之前的数组：");
    for (int i = 0; i < n; i++) {
      System.out.print(a[i] + " ");
    }
    for (int i = 0; i < n / 2; i++) {
      int temp = a[i];
      a[i] = a[n - 1 - i];
      a[n - 1 - i] = temp;
    }
    System.out.println();
    System.out.println("交换之后的数组：");
    for (int i = 0; i < n; i++) {
      System.out.print(a[i] + " ");
    }
  }
}