如何在java中将树结构转换为节点流 [英] How to convert a tree structure to a Stream of nodes in java

问题描述

我想在 Java8 节点流中转换树.

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

这是一个存储数据的节点树，可供选择:

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

public class SelectTree<D> {

  private D data;

  private boolean selected = false;

  private SelectTree<D> parent;

  private final List<SelectTree<D>> children = new ArrayList<>();

  public SelectTree(D data, SelectTree<D> parent) {
    this.data = data;
    if (parent != null) {
      this.parent = parent;
      this.parent.getChildren().add(this);
    }
  }

  public D getData() {
    return data;
  }

  public void setData(D data) {
    this.data = data;
  }

  public boolean isSelected() {
    return selected;
  }

  public void setSelected(boolean selected) {
    this.selected = selected;
  }

  public SelectTree<D> getParent() {
    return parent;
  }

  public void setParent(SelectTree<D> parent) {
    this.parent = parent;
  }

  public List<SelectTree<D>> getChildren() {
    return children;
  }

  public boolean isRoot() {
    return this.getParent() == null;
  }

  public boolean isLeaf() {
    return this.getChildren() == null || this.getChildren().isEmpty();
  }
}

我想获取所选数据的集合

I want to get a collection of the selected data

我想做这样的事情:

  public static void main(String[] args) {
    SelectTree<Integer> root = generateTree();
    
    List<Integer> selectedData = root.stream()
            .peek(node -> System.out.println(node.getData()+": "+node.isSelected()))
            .filter(node-> node.isSelected())
            .map(node-> node.getData())
            .collect(Collectors.toList()) ;
    
    System.out.println("
selectedData="+selectedData);
  }

  private static SelectTree<Integer> generateTree() {
    SelectTree<Integer> n1 = new SelectTree(1, null);
    SelectTree<Integer> n11 = new SelectTree(11, n1);
    SelectTree<Integer> n12 = new SelectTree(12, n1);
    n12.setSelected(true);
    SelectTree<Integer> n111 = new SelectTree(111, n11);
    n111.setSelected(true);
    SelectTree<Integer> n112 = new SelectTree(112, n11);
    SelectTree<Integer> n121 = new SelectTree(121, n12);
    SelectTree<Integer> n122 = new SelectTree(122, n12);
    return n1;
  }

问题是找到 stream() 的实现，我想我可以帮助一些人分享我的解决方案，我很想知道是否有一些问题或更好的方法来做到这一点.

The problem was to find the implementation of stream() and I think I could help some people sharing my solution and I would be interested in knowing if there are some issues or better ways of doing this.

起初是针对primefaces TreeNode，但我将问题推广到各种树.

At first it was for primefaces TreeNode but I generalize the problem to all kinds of trees.

推荐答案

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)) ;
    }
  }

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