在Java中将层次结构列表转换为平面列表

我有一个如下所示的分层list，我想将其转换为平面list.

I have a hierarchical list like below and I want to convert it to a flat list.

我写了一个叫做convertToFlatList的方法并使用了它.但是最终结果中缺少一些要素.我做错了什么?

I have wrote a method called convertToFlatList and have used it. But some elements are missing in the final results. What did i do wrong?

还有比我以前将列表转换为平面列表更好的方法吗?

Also is there a better way than the way I have used to convert my list to a flat list?

我添加了示例代码和类似于我在场景中必须使用的对象的东西.最终结果应为1、2、3、4、5、6、7

I have added a sample code and something similar to the Objects I have to used in my scenario. Final result should be 1, 2, 3, 4, 5, 6, 7

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

public class Main
{
  public static void main(String[] args)
  {
    Member memberOne = new Member(1);
    Member memberTwo = new Member(2);
    Member memberThree = new Member(3);
    Member memberFour = new Member(4);
    Member memberFive = new Member(5);
    Member memberSix = new Member(6);
    Member memberSeven = new Member(7);

    memberTwo.setChildren(Arrays.asList(memberThree, memberFour));
    memberFour.setChildren(Arrays.asList(memberFive, memberSix));

    List<Member> memberList = Arrays.asList(memberOne, memberTwo, memberSeven);
    List<Member> flatList = new ArrayList<>();
    List<Member> convertedList = convertToFlatList(memberList, flatList);
    System.out.println(convertedList);
  }

  private static List<Member> convertToFlatList(List<Member> memberList, List<Member> flatList)
  {
    for (Member member : memberList)
    {
      if (member.getChildren() != null)
      {
        convertToFlatList(member.getChildren(), flatList);
      }
      else
      {
        flatList.add(member);
      }
    }
    return flatList;
  }
}

class Member
{
  private List<Member> children;

  private int memberId;

  Member(int memberId)
  {
    this.memberId = memberId;
  }

  List<Member> getChildren()
  {
    return children;
  }

  void setChildren(List<Member> children)
  {
    this.children = children;
  }

  int getMemberId()
  {
    return memberId;
  }

  void setMemberId(int memberId)
  {
    this.memberId = memberId;
  }

  @Override
  public String toString()
  {
    return String.valueOf(this.memberId);
  }
}