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


public class ListExample {
	
	public static void reverse(List list) {
		int x = 0;
		int y = list.size()-1;
		while (x < y) {
			Object tmp = list.get(x);
			list.set(x, list.get(y));
			list.set(y, tmp);
			++x;
			--y;
		}
	}

	public static void main(String[] args) {

		List list = new ArrayList();

		for (int i=0; i < 20; ++i) {
			list.add(new Integer(i));
		}

		System.out.println(list.toString());

		reverse(list);

		System.out.println(list.toString());
	}


}