for循环创建树类结构

package com.zhlc.tree;

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

/**
* author：dwj <br>
* desc： <br>
* date： 2015-12-1 上午10:29:47<br>
*/
public class Tree {
    private int id;
    private String name;
    private int parentId;
    private List<Tree> childrens;
    public Tree(int id,String name,int parentId){
        this.id = id;
        this.name = name;
        this.parentId = parentId;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getParentId() {
        return parentId;
    }
    public void setParentId(int parentId) {
        this.parentId = parentId;
    }
    public List<Tree> getChildrens() {
        return childrens;
    }
    public void setChildrens(List<Tree> childrens) {
        this.childrens = childrens;
    }
    @Override
    public String toString() {
        return "Tree [id=" + id + ", name=" + name + ", parentId=" + parentId
                + ", childrens=" + childrens + "]";
    }
    public static void main(String[] args) {
    Tree tree1 = new Tree(1, "顶层节点1", 0);
    Tree tree2 = new Tree(2, "顶层节点2", 0);
    Tree tree3 = new Tree(3, "顶层节点3", 0);
        
    Tree tree4 = new Tree(4, "二级节点4", 1);
    Tree tree5 = new Tree(5, "二级节点5", 2);
    Tree tree6 = new Tree(6, "二级节点6", 3);
        
    Tree tree7 = new Tree(7, "三级节点7", 4);
    Tree tree8 = new Tree(8, "三级节点8", 4);
    Tree tree9 = new Tree(9, "三级节点9", 5);
        
        List<Tree> trees = new ArrayList<Tree>();
        trees.add(tree9);
        trees.add(tree8);
        trees.add(tree7);
        trees.add(tree6);
        trees.add(tree5);
        trees.add(tree4);
        trees.add(tree3);
        trees.add(tree2);
        trees.add(tree1);

        List<Tree> rootTrees = new ArrayList<Tree>();
        for (Tree tree : trees) {
            if(tree.getParentId() == 0){
                rootTrees.add(tree);
            }
            for (Tree t : trees) {
                if(t.getParentId() == tree.getId()){
                    if(tree.getChildrens() == null){
                        List<Tree> myChildrens = new ArrayList<Tree>();
                        myChildrens.add(t);
                        tree.setChildrens(myChildrens);
                    }else{
                        tree.getChildrens().add(t);
                    }
                }
            }
        }
       
        for (Tree tree : rootTrees) {
            System.out.println(tree.toString());
        }
        
    }
}