arraylist Java迭代列表

Question

你如何迭代一个包含“父/子/孙/等”的列表

样本数据：

{ID，父ID}

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

名单是{parent, childA, childB, grandChildA, grandChildB}

如何用“根”来迭代它

样本输出：

• 家长
  • 奇尔达
    • 孙女
  • ChildB
    • 孙女

谢谢

样本数据：

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);

然后我将这些对象放在ArrayList:ArrayList testList中

所以，问题是，如何迭代列表，这样结果会：

• 家长
  • 奇尔达
    • 孙女
  • ChildB
    • 孙女

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