Question

如何迭代具有“parent / child / grandChild / etc。”的列表？

示例数据：

{ID，Parent ID}

Object parent = {1, 0};
Object childA = {2, 1};
Object childB = {3, 1};
Object grandChildA = {4, 3};
Object grandChildB = {5, 2};

列表是{parent, childA, childB, grandChildA, grandChildB}

你如何通过“根”进行迭代？

示例输出：

父
- ChildA
  - GrandChildB
- ChildB
  - GrandChildA

谢谢！

示例数据：

构造函数：SampleObject(int id,int parentId)

SampleObject parent = new SampleObject(1, 0);
SampleObject childA = new SampleObject(2, 1);
SampleObject childB = new SampleObject(3, 1);
SampleObject grandChildA = new SampleObject(4, 3);
SampleObject grandChildB = new SampleObject(5, 2);

然后我将对象放在ArrayList：ArrayList testList

中

所以，问题是，如何遍历列表，以便结果如下：

父
- ChildA
  - GrandChildB
- ChildB
  - GrandChildA

Answer 1

我建议使用树状数据结构，例如：

package com.stackoverflow.test;

import java.util.ArrayList;
import java.util.List;

public class TreeNode {
   private String         name       = "";
   private List<TreeNode> childNodes = new ArrayList<TreeNode>();

   public TreeNode(final String name) {
      this.name = name;
   }

   public String getName() {
      return this.name;
   }

   public void add(final TreeNode child) {
      childNodes.add(child);
   }

   public List<TreeNode> getChildren() {
      return this.childNodes;
   }

   public static void main(String[] args) {

      TreeNode parent = new TreeNode("Parent");

      TreeNode childA = new TreeNode("ChildA");
      childA.add(new TreeNode("GrandChildA"));

      TreeNode childB = new TreeNode("ChildB");
      childB.add(new TreeNode("GrandChildB"));

      parent.add(childA);
      parent.add(childB);

      TreeNode.printRecursively(parent, 0);
   }

   private static void printRecursively(final TreeNode root, final int level) {
      if (null != root && null != root.getChildren()) {

         for (int i = 0; i < level; ++i) {
            System.out.print("   ");
         }

         System.out.println(root.getName());

         for (TreeNode child: root.getChildren()) {
            TreeNode.printRecursively(child, level + 1);
         }
      }
   }

}

将打印：

Parent
   ChildA
      GrandChildA
   ChildB
      GrandChildB

Java迭代列表

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