39-综合实战：一对多映射

    按照表的要求将表的结构转换为类结构，同时可以获取如下信息：

• 获取一个分类的完整信息；

• 可以根据分类获取其对应的所有子分类的信息。

范例：

class Item{
    private long iid;
    private String title;
    private Subitem subitems []; //多个子分类
    public Item(long iid,String title){
        this.iid = iid;
        this.title = title;
    }
    public void setSubitems(Subitem[] subitems){
        this.subitems = subitems;
    }
    public Subitem[] getSubitems(){
        return this.subitems;
    }
    // setter、getter、无参构造略
    public String getInfo(){
        return "【分类信息】iid = " + this.iid + "、title = " + this.title;
    }
}
class Subitem{
    private long sid;
    private String title;
    private Item item;  //分类
    public Subitem(long sid,String title){
        this.sid = sid;
        this.title = title;
    }
    //  setter、getter、无参构造略
    public String getInfo(){
        return "【子分类信息】sid =" + this.sid + "、title = " + this.title;
    }
    public void setItem(Item item){
        this.item = item;
    }
    public Item getItem(){
        return this.item;
    }
}
public class JavaDemo{
    public static void main(String args[]){
        //第一步：根据结构设置对象数据
        Item item = new Item(1L,"图书");
        Subitem subitems[] = new Subitem[]{
            new Subitem(10L, "编程图书"),
            new Subitem(11L, "图形图像类图书"),
            new Subitem(12L, "文学图书"),
            new Subitem(13L, "漫画图书"),
        };
        item.setSubitems(subitems);
        for(int x = 0; x < subitems.length; x++){
            subitems[x].setItem(item);
        }
        //第二步：根据要求获取数据
        System.out.println(item.getInfo());
        for(int x = 0; x < item.getSubitems().length; x++){
            System.out.println("\t|- " + item.getSubitems()[x].getInfo());
        }
    }   
}