How to convert a tree structure to a Stream of nodes in java

Question

I want to convert a tree in a Java8 stream of nodes.

Here is a tree of nodes storing data which can be selected:

public class SelectTree {

           


        

Answer 1

One small addition to kwisatz's answer.

This implementation:

this.getChildren().stream()
        .map(SelectTree::stream)
        .reduce(Stream.of(this), Stream::concat);

will be more eager, i. e. the whole hierarchy will be traversed during a stream creation. If your hirarchy is large and, let's say, you're looking for a single node matching some predicate, you may want a more lazy behaviour:

Stream.concat(Stream.of(this),
              this.getChildren().stream().flatMap(SelectTree::stream));

In this case, only the children of the root node will be retrieved during a stream creation, and a search for a node won't necessarily result in the whole hierarchy being traversed.

Both approaches will exhibit the DFS iteration order.