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

I find this implementation of stream() which is a DFS tree traversal:

public class SelectTree {

  //...

  public Stream> stream() {
    if (this.isLeaf()) {
      return Stream.of(this);
    } else {
      return this.getChildren().stream()
                .map(child -> child.stream())
                .reduce(Stream.of(this), (s1, s2) -> Stream.concat(s1, s2));
    }
  }
}

If you can't change the tree implementation like for primefaces TreeNode (org.primefaces.model.TreeNode) you can define a method in an other class:

  public Stream stream(TreeNode parentNode) {
    if(parentNode.isLeaf()) {
      return Stream.of(parentNode);
    } else {
      return parentNode.getChildren().stream()
                .map(childNode -> stream(childNode))
                .reduce(Stream.of(parentNode), (s1, s2) -> Stream.concat(s1, s2)) ;
    }
  }