Convert hierarchical list to a flat list in java

Question

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

I have wrote a method called convertToFlatList

Answer 1

If you use Java 8, just add this method to the Member class:

public Stream streamAll(){
    if(getChildren() == null){
        return Stream.of(this);
    }
    return Stream.concat(Stream.of(this), getChildren().stream().flatMap(Member::streamAll));
}

Alternatively, you can remove the null check if you always initialize children to an empty list :

public Stream streamAll(){
    return Stream.concat(Stream.of(this), getChildren().stream().flatMap(Member::streamAll));
}

Then to get the flat list:

List convertedList = memberList.stream()
                                       .flatMap(Member::streamAll)
                                       .collect(Collectors.toList());