Combine 、 intersection 、 Difference set 、 What is the concept of complement ？

  One 、 rely on

    <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-collections4</artifactId>
            <version>4.4</version>
        </dependency>

Two 、 Tool class

import org.apache.commons.collections4.CollectionUtils;

import java.util.List;

public class ListUtils {
    // Get the union of two sets （ Automatic weight removal ）
    public static  <T> List<T> getUnion(List<T> list1, List<T> list2){
        List<T> union = (List<T>) CollectionUtils.union(list1, list2);
        return union;
    }

    // Get the intersection of two sets 
    public static  <T> List<T> getIntersection(List<T> list1,List<T> list2){
        List<T> intersection = (List<T>) CollectionUtils.intersection(list1, list2);
        return intersection;
    }
    // Gets the complement of the intersection of two sets   namely  list1 + list2 -  intersection 
    public static  <T> List<T> getDisjunction(List<T> list1,List<T> list2){
        List<T> disjunction = (List<T>)CollectionUtils.disjunction(list1, list2);
        return disjunction;
    }

    // Get the difference set of two sets  list1 -  intersection 
    public static  <T> List<T> getSubtract(List<T> list1,List<T> list2){
        List<T> subtract = (List<T>)CollectionUtils.subtract(list1, list2);
        return subtract;
    }
}

3、 ... and 、 test

public static void main(String[] args) {
        List<Integer> list1 = Stream.of(1, 2, 3).collect(Collectors.toList());
        List<Integer> list2 = Stream.of(2, 3, 4).collect(Collectors.toList());

        System.out.println("list1:" + list1);
        System.out.println("list2:" + list2);
        List<Integer> union = getUnion(list1, list2);
        System.out.println("list1-list2 Combine union：" + union);

        List<Integer> intersection = getIntersection(list1, list2);
        System.out.println("list1,-list2 intersection ：" + intersection);

        List<Integer> disjunction = getDisjunction(list1, list2);
        System.out.println("list1-list2 Complement of intersection ：" + disjunction);

        List<Integer> subtract = getSubtract( union,list1);
        System.out.println("union-list1 Difference set ：" + subtract);

    }

list1:[1, 2, 3]
list2:[2, 3, 4]
list1-list2 Combine union：[1, 2, 3, 4]
list1,-list2 intersection ：[2, 3]
list1-list2 Complement of intersection ：[1, 4]
union-list1 Difference set ：[4]