List的交集并集差集.

list
1) 并集

public List<String> removeDuplicate(List<String> list1, List<String> list2)
{
List<String> list = new ArrayList<String>();
list.addAll(list1);
list.addAll(list2);
HashSet<String> hs = new HashSet<String>(list);
list.clear();
list.addAll(hs);
return list;
}
2) 交集

public List<String> retainAll(List<String> list1, List<String> list2)
{
List<String> list = new ArrayList<String>();
list.addAll(list1);
list.retainAll(list2);
return list;
}

3) 差集

public List<String> subtraction(List<String> list1, List<String> list2)
{
List<String> list = new ArrayList<String>();
list.addAll(list1);
list.removeAll(list2);
return list;
}