一、程式碼

public class LambdaDemo {
    public static void main(String[] args) {

        List<User> list1 = Arrays.asList(
                new User(1, "mao", 22),
                new User(2, "xiaomao", 23),
                new User(3, "xiaomaomao", 24),
                new User(4, "xiaoxiaomaomao", 25)
        );

        List<User> list2 = Arrays.asList(
                new User(1, "mao", 22),
                new User(2, "xiaomao", 23),
                new User(3, "xiaomaomao", 24)
        );

        // 兩個集合的重複部分
        List<User> duplicateList = list1.stream().filter((item) -> list2.stream().map((item2) -> item2.getId()).collect(Collectors.toList()).contains(item.getId())).collect(Collectors.toList());
        // 兩個集合的差集 (list1-list2)
        List<User> differentList = list1.stream().filter((item) -> !list2.stream().map((item2) -> item2.getId()).collect(Collectors.toList()).contains(item.getId())).collect(Collectors.toList());

        System.out.println("重複的元素為: " + duplicateList);

        System.out.println("兩個集合的差集為: " + differentList);
    }
}
 

二、測試