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

A more general approach using any node class is to add a parameter for the method, which returns the children:

public class TreeNodeStream {
  public static  Stream of(T node, Function> childrenFunction) {
    return Stream.concat( //
      Stream.of(node), //
      childrenFunction.apply(node).stream().flatMap(n -> of(n, childrenFunction)));
  }
}

An example using File:

TreeNodeStream.of(
  new File("."), f -> f.isDirectory() ? Arrays.asList(f.listFiles()) :
                                        Collections.emptySet())
  .filter(f -> f.getName().endsWith(".java"))
  .collect(Collectors::toList);