opid's document

ArrayList 합집합(union)

	public <T> List<T> union(List<T> list1, List<T> list2) {
		Set<T> set = new HashSet<T>();

		set.addAll(list1);
		set.addAll(list2);

		return new ArrayList<T>(set);
	}

ArrayList 교집합(intersection)

	public <T> List<T> intersection(List<T> list1, List<T> list2) {
		List<T> list = new ArrayList<T>();

		for (T t : list1) {
			if (list2.contains(t)) {
				list.add(t);
			}
		}

		return list;
	}

사용예시

public class ListUtil {

	public static void main(String... args) throws Exception {

		List<String> list1 = new ArrayList<String>(Arrays.asList("A", "B", "C"));
		List<String> list2 = new ArrayList<String>(Arrays.asList("B", "C", "D",
				"E", "F"));

		System.out.println("교집합" + new ListUtil().intersection(list1, list2));
		System.out.println("합집합" + new ListUtil().union(list1, list2));
	}

	public <T> List<T> union(List<T> list1, List<T> list2) {
		Set<T> set = new HashSet<T>();

		set.addAll(list1);
		set.addAll(list2);

		return new ArrayList<T>(set);
	}

	public <T> List<T> intersection(List<T> list1, List<T> list2) {
		List<T> list = new ArrayList<T>();

		for (T t : list1) {
			if (list2.contains(t)) {
				list.add(t);
			}
		}

		return list;
	}
}