import java.util.*;

public class Ex02SwapPairs {

	public static void swapPairs(List<String> list) {
		for (int i = 0; i < list.size(); i+=2) {
			if (i+1 < list.size()) {
				String s1 = list.get(i);
				String s2 = list.get(i+1);
				list.set(i,s2);
				list.set(i+1,s1);
			}
		}
	}

	public static void main(String[] args) {
		String[] strs =
			{ "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11" };
		List<String> list = new ArrayList<String>(
			Arrays.asList(strs)
		);
		System.out.println(list.toString());
		swapPairs(list);
		System.out.println(list.toString());
	}

}