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());
}

}
}