import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ArrayReverse {
    // ArrayList 反转元素
    // 双指针解法
    // 出自 java.util.Collections#reverse
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7));
        int size = list.size();
        Integer x, y;
        for (int begin = 0, mid = size >> 1, end = size - 1; begin < mid; begin++, end--) {
            x = list.get(begin);
            y = list.get(end);
            list.set(begin, y);
            list.set(end, x);
        }
        System.out.println(list);
    }
}