java - 从流中获取父对象

Question

我有这门课:

public class StructUserType extends UserType {

    MembersList membersList = new MembersList();

    public List<Member> getMembers() {
        return Collections.unmodifiableList(membersList.members);
    }

    static class MembersList {
        List<Member> members = new ArrayList<>();
    }

    public static class Member implements Identifiable {
        private Integer id;

        public Integer getId() {
            return id;
        }
    }    
} 

我有一个 List 对象:

List<SmbpUserType> userTypes = new ArrayList<>();

我想找到等于某个 id 的 Member。我试过如下:

Integer id = 1;
userTypes.stream()
                .filter(StructUserType.class::isInstance)
                .map(StructUserType.class::cast)
                .forEach(structUserType -> {
                    structUserType.getMembers()
                            .stream()
                            .filter(m -> m.getId() == id)
                            .findFirst().orElse(null);
                });

我想，当内部流中的过滤器运行并找到第一个成员时，返回该成员包含的父元素，那些 UserType。

经典风格的模拟:

for (UserType userType : userTypes) {
            if (userType instanceof StructUserType) {
                List<StructUserType.Member> members = ((StructUserType) userType).getMembers();

                for (StructUserType.Member member : members) {
                    if (member.getId() == id) {
                        return userType;
                    }
                }
            }
        }
        return null;

Answer 1

用filter替换forEach，寻找满足内部流管道条件的StructUserType实例。然后获取 Stream 的第一个元素(如果存在)。

return
   userTypes.stream()
            .filter(StructUserType.class::isInstance)
            .map(StructUserType.class::cast)
            .filter(st -> st.getMembers()
                            .stream()
                            .anyMatch(m -> m.getId().equals(id)))
            .findFirst()
            .orElse(null);