我发现 stream() 的这个实现是一个 DFS 树遍历:

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

public class SelectTree<D> {

  //...

  public Stream<SelectTree<D>> 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));
    }
  }
}

如果你不能像 primefaces TreeNode (org.primefaces.model.TreeNode) 那样更改树的实现，你可以在其他类中定义一个方法:

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<TreeNode> 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)) ;
    }
  }