java定义几个类和ArrayList，存储读如下结构的数据？？

有类似如下的结构，有A1，A2,A2...。A1下一级有B1,B2,B3..。B1下面有C1，C2等。。

怎么定义几个类和ArrayList，把这种结构的数据存储到ArrayList中。

再去把ArrayList中按照如上结构存储的数据读出来.

图片说明

这种多层次的结构建议你用树形结构进行存储。定义的实体类只需要两个，并且所有数据也可以保存在数据库的一张表里，下面给你举个简单的例子：
假如说你的实体为Menu，定义一个实体类：

public class Menu {

    /**
     * 主键ID。
     */
    private String id;

    /**
     * 名称。
     */
    private String name;

    /**
     * 父ID。
     */
    private String parentId;// 父ID

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getParentId() {
        return parentId;
    }

    public void setParentId(String parentId) {
        this.parentId = parentId;
    }
}

再定义一个树形实体，代码如下：

public class Tree<T> {

    /**
     * 节点ID。
     */
    private String id;

    /**
     * 显示节点名称。
     */
    private String name;

    /**
     * 节点的子节点。
     */
    private List<Tree<T>> child = new ArrayList<>();

    /**
     * 父ID。
     */
    private String parentId;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Tree<T>> getChild() {
        return child;
    }

    public void setChild(List<Tree<T>> child) {
        this.child = child;
    }

    public String getParentId() {
        return parentId;
    }

    public void setParentId(String parentId) {
        this.parentId = parentId;
    }

    /**
     * 声明。
     * 
     * @param id 参数
     * @param name 参数
     * @param child 参数
     * @param parentId 参数
     */

    public Tree(String id, String name,  List<Tree<T>> child, String parentId) {
        super();
        this.id = id;
        this.name = name;
        this.child = child;
        this.parentId = parentId;
    }

    public Tree() {
        super();
    }

    @Override
    public String toString() {

        return JSON.toJSONString(this);
    }

}

数据中的数据存储如下：

图片说明

下面将数据库中的数据查出，并转化为树形菜单，首先将menu表中所有的数据查出来放到List

menu中（这步不做过多叙述），然后
通过getMenuTree()方法转为树形结构

    private static List<Menu> getMenuTree(List<Menu> menu) {
        List<Tree<Menu>> trees = new ArrayList<>();
        for (Menu m : menu) {
            Tree<Menu> tree = new Tree<>();
            tree.setId(m.getId());
            tree.setParentId(m.getParentId());
            tree.setName(m.getName());
            trees.add(tree);
        }
        List<Tree<Menu>> t = BuildTree.buildList(trees, "");
        return t;
    }

java list实现树形结构

1.javabean

import java.util.List;

public class TreeNode {

private String id;

private String parentId;

private String name;

private List children;

public TreeNode(String id, String name, String parentId) {
this.id = id;
this.parentId = parentId;
this.name = name;
}
public TreeNode(String id, String name, TreeNode parent) {
this.id = id;
this.parentId = parent.getId();
this.name = name;
}

public String getParentId() {
return parentId;
}

public void setParentId(String parentId) {
this.parentId = parentId;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getId() {
return id;
}

public void setId(String id) {
this.id = id;
}

public List getChildren() {
return children;
}

public void setChildren(List children) {
this.children = children;
}

@Override
public String toString() {
return "TreeNode{" +
"id='" + id + '\'' +
", parentId='" + parentId + '\'' +
", name='" + name + '\'' +
", children=" + children +
'}';
}

}

2.方法

import java.util.ArrayList;
import java.util.List;
public class TreeBuilder {

/**

两层循环实现建树
@param treeNodes 传入的树节点列表
@return */ public static List bulid(List treeNodes) {

List trees = new ArrayList();

for (TreeNode treeNode : treeNodes) {

if ("0".equals(treeNode.getParentId())) {
trees.add(treeNode);
}

for (TreeNode it : treeNodes) {
if (it.getParentId() == treeNode.getId()) {
if (treeNode.getChildren() == null) {
treeNode.setChildren(new ArrayList());
}
treeNode.getChildren().add(it);
}
}
}
return trees;
}

/**

使用递归方法建树
@param treeNodes
@return */ public static List buildByRecursive(List treeNodes) { List trees = new ArrayList(); for (TreeNode treeNode : treeNodes) { if ("0".equals(treeNode.getParentId())) { trees.add(findChildren(treeNode,treeNodes)); } } return trees; }

/**

递归查找子节点
@param treeNodes
@return */ public static TreeNode findChildren(TreeNode treeNode,List treeNodes) { for (TreeNode it : treeNodes) { if(treeNode.getId().equals(it.getParentId())) { if (treeNode.getChildren() == null) { treeNode.setChildren(new ArrayList()); } treeNode.getChildren().add(findChildren(it,treeNodes)); } } return treeNode; }

public static void main(String[] args) {

TreeNode treeNode1 = new TreeNode("1","广州","0");
TreeNode treeNode2 = new TreeNode("2","深圳","0");

TreeNode treeNode3 = new TreeNode("3","天河区",treeNode1);
TreeNode treeNode4 = new TreeNode("4","越秀区",treeNode1);
TreeNode treeNode5 = new TreeNode("5","黄埔区",treeNode1);
TreeNode treeNode6 = new TreeNode("6","石牌",treeNode3);
TreeNode treeNode7 = new TreeNode("7","百脑汇",treeNode6);

TreeNode treeNode8 = new TreeNode("8","南山区",treeNode2);
TreeNode treeNode9 = new TreeNode("9","宝安区",treeNode2);
TreeNode treeNode10 = new TreeNode("10","科技园",treeNode8);

List list = new ArrayList();

list.add(treeNode1);
list.add(treeNode2);
list.add(treeNode3);
list.add(treeNode4);
list.add(treeNode5);
list.add(treeNode6);
list.add(treeNode7);
list.add(treeNode8);
list.add(treeNode9);
list.add(treeNode10);
3.测试
List trees = TreeBuilder.bulid(list);
for (int i = 0; i < trees.size(); i++) {
System.out.println(trees.get(i));
}
List trees_ = TreeBuilder.buildByRecursive(list);
for (int i = 0; i <trees.size(); i++) {
System.out.println(trees.get(i));
}
}

}

4.数据

TreeNode{id='1', parentId='0', name='广州', children=[TreeNode{id='3', parentId='1', name='天河区', children=[TreeNode{id='6', parentId='3', name='石牌', children=[TreeNode{id='7', parentId='6', name='百脑汇', children=null}]}]}, TreeNode{id='4', parentId='1', name='越秀区', children=null}, TreeNode{id='5', parentId='1', name='黄埔区', children=null}]}
TreeNode{id='2', parentId='0', name='深圳', children=[TreeNode{id='8', parentId='2', name='南山区', children=[TreeNode{id='10', parentId='8', name='科技园', children=null}]}, TreeNode{id='9', parentId='2', name='宝安区', children=null}]}
TreeNode{id='1', parentId='0', name='广州', children=[TreeNode{id='3', parentId='1', name='天河区', children=[TreeNode{id='6', parentId='3', name='石牌', children=[TreeNode{id='7', parentId='6', name='百脑汇', children=null}, TreeNode{id='7', parentId='6', name='百脑汇', children=null}]}, TreeNode{id='6', parentId='3', name='石牌', children=[TreeNode{id='7', parentId='6', name='百脑汇', children=null}, TreeNode{id='7', parentId='6', name='百脑汇', children=null}]}]}, TreeNode{id='4', parentId='1', name='越秀区', children=null}, TreeNode{id='5', parentId='1', name='黄埔区', children=null}, TreeNode{id='3', parentId='1', name='天河区', children=[TreeNode{id='6', parentId='3', name='石牌', children=[TreeNode{id='7', parentId='6', name='百脑汇', children=null}, TreeNode{id='7', parentId='6', name='百脑汇', children=null}]}, TreeNode{id='6', parentId='3', name='石牌', children=[TreeNode{id='7', parentId='6', name='百脑汇', children=null}, TreeNode{id='7', parentId='6', name='百脑汇', children=null}]}]}, TreeNode{id='4', parentId='1', name='越秀区', children=null}, TreeNode{id='5', parentId='1', name='黄埔区', children=null}]}
TreeNode{id='2', parentId='0', name='深圳', children=[TreeNode{id='8', parentId='2', name='南山区', children=[TreeNode{id='10', parentId='8', name='科技园', children=null}, TreeNode{id='10', parentId='8', name='科技园', children=null}]}, TreeNode{id='9', parentId='2', name='宝安区', children=null}, TreeNode{id='8', parentId='2', name='南山区', children=[TreeNode{id='10', parentId='8', name='科技园', children=null}, TreeNode{id='10', parentId='8', name='科技园', children=null}]}, TreeNode{id='9', parentId='2', name='宝安区', children=null}]}