快速得到两个list中不同部分的list

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TesList {
	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		list.add("123");
		list.add("456");
		list.add("789");

		List<String> list2 = new ArrayList<String>();
		list2.add("123");
		list2.add("456");
		list2.add("789");
		list2.add("xxxx");
		list2.add("yyyy");


		List<String>list3= getDiffrent(list, list2);
		for (String string : list3) {
			System.out.println(string);
		}
	}

	private static List<String> getDiffrent(List<String> list1,
			List<String> list2) {
		long st = System.nanoTime();
		Map<String, Integer> map = new HashMap<String, Integer>(list1.size()
				+ list2.size());
		List<String> diff = new ArrayList<String>();
		for (String string : list1) {
			map.put(string, 1);
		}
		for (String string : list2) {
			Integer cc = map.get(string);
			if (cc != null)
			{
				map.put(string, ++cc);
				continue;
			}
			map.put(string, 1);
		}
		for (Map.Entry<String, Integer> entry : map.entrySet())
		{
			if (entry.getValue() == 1)
			{
				diff.add(entry.getKey());
			}
		}
		System.out.println("getDiffrent total times "
				+ (System.nanoTime() - st));
		return diff;

	}
}