Intersection and union of ArrayLists in Java

Question

Are there any methods to do so? I was looking but couldn\'t find any.

Another question: I need these methods so I can filter files. Some are AND filter

Answer 1

Here's a plain implementation without using any third-party library. Main advantage over retainAll, removeAll and addAll is that these methods don't modify the original lists input to the methods.

public class Test {

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

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

        System.out.println(new Test().intersection(list1, list2));
        System.out.println(new Test().union(list1, list2));
    }

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

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

        return new ArrayList(set);
    }

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

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

        return list;
    }
}