java如何获取两个List集合之间的交集、差集、并集

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Test {
    public static void main(String[] args) {
        List<String> list1 = new ArrayList<>(Arrays.asList("a","b","c"));

        List<String> list2 = new ArrayList<>(Arrays.asList("b","c","d"));

        System.out.println("交集："+intersect(list1,list2));
        System.out.println("差集："+minus(list1,list2));
        System.out.println("并集："+union(list1,list2));
    }

    /**
     * 交集
     * @param list1
     * @param list2
     * @return
     */
    private static List<String> intersect(List<String> list1, List<String> list2) {
        List<String> intersect = list1.stream().filter(item -> list2.contains(item)).collect(Collectors.toList());
        return intersect;
    }

    /**
     * 差集（list1-list2）
     * @param list1
     * @param list2
     * @return
     */
    private static List<String> minus(List<String> list1, List<String> list2) {
        List<String> minus = list1.stream().filter(item -> !list2.contains(item)).collect(Collectors.toList());
        return minus;
    }

    /**
     * 并集（不去重）
     * @param list1
     * @param list2
     * @return
     */
    private static List<String> unionAll(List<String> list1, List<String> list2) {
        list1.addAll(list2);
        return list1;
    }

    /**
     * 并集（去重）
     * @param list1
     * @param list2
     * @return
     */
    private static List<String> union(List<String> list1, List<String> list2) {
        list1.addAll(list2);
        return list1.stream().distinct().collect(Collectors.toList());
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        List<String> list1 = new ArrayList<>(Arrays.asList("a","b","c"));

        List<String> list2 = new ArrayList<>(Arrays.asList("b","c","d"));

        // boolean retainAll 删除两个集合不同的元素
        // 注意：此操作会直接删除list1中的元素
        System.out.println(list1.retainAll(list2));
        System.out.println("集合1："+list1);
        System.out.println("集合2："+list2);
    }
}

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

import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.lang3.ArrayUtils;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Test {
    public static void main(String[] args) {
        List<String> list1 = new ArrayList<>(Arrays.asList("a","b","c"));

        List<String> list2 = new ArrayList<>(Arrays.asList("b","c","d"));

        //intersection: 取交集
        List<String> sameList = CollectionUtils.intersection(list1,list2).stream().collect(Collectors.toList());
        System.out.println("交集："+sameList);

        //取并集（去重）
        System.out.println("并集："+ ArrayUtils.toString(CollectionUtils.union(list1,list2)));

        //取差集
        System.out.println("差集："+CollectionUtils.subtract(list1,list2));

        //取两个集合的交集的补集(补集一般指绝对补集，即一般地，设S是一个集合，A是S的一个子集，由S中所有不属于A的元素组成的集合，叫做子集A在S中的绝对补集)
        System.out.println("补集："+CollectionUtils.disjunction(list1,list2));
    }

}