访问者模式

/**
 * 抽象元素类 商品
 */
public interface Product
{
    /**
     * 用于接受访问者的访问
     */
    void accept(Visitor visitor);
}
 
 
/**
 * 抽象访问者类Visitor
 */
public abstract class Visitor
{
    protected String name;
 
    public void setName(String name)
    {
        this.name = name;
    }
 
    public abstract void visit(Apple apple);
 
    public abstract void visit(Book book);
}
 
 
/**
 * 具体元素类 苹果类
 */
public class Apple implements Product
{
 
    /**
     * 用于接受访问者的访问
     */
    @Override
    public void accept(Visitor visitor)
    {
        visitor.visit(this);
    }
}
 
/**
 * 具体元素类 书籍类
 */
public class Book implements Product
{
    @Override
    public void accept(Visitor visitor)
    {
        visitor.visit(this);
    }
}
 
import java.util.ArrayList;
import java.util.Iterator;
 
/**
 * 购物车类
 */
public class BuyBasket
{
    private ArrayList list = new ArrayList();
 
    public void accept(Visitor visitor)
    {
        Iterator i = list.iterator();
        while (i.hasNext())
        {
            ((Product) i.next()).accept(visitor);
        }
    }
 
    //添加商品
    public void addProduct(Product product)
    {
        list.add(product);
    }
 
    //移除商品
    public void removeProduct(Product product)
    {
        list.remove(product);
    }
}
 
/**
 * 具体访问者类 顾客
 */
public class Customer extends Visitor
{
 
    @Override
    public void visit(Apple apple)
    {
        System.out.println("顾客" + name + "选苹果");
    }
 
    @Override
    public void visit(Book book)
    {
        System.out.println("顾客" + name + "买书");
    }
}
 
/**
 * 具体访问者类 打包员
 */
public class Packager extends Visitor
{
 
    @Override
    public void visit(Apple apple)
    {
        System.out.println("打包员" + name + "将苹果打包");
    }
 
    @Override
    public void visit(Book book)
    {
        System.out.println("打包员" + name + "将书打包");
    }
}
 
/**
 * 具体访问者类 收银员
 */
public class Saler extends Visitor
{
    @Override
    public void visit(Apple apple)
    {
        System.out.println("收银员" + name + "给苹果过秤，然后计算价格。");
    }
 
    @Override
    public void visit(Book book)
    {
        System.out.println("收银员" + name + "直接计算书的价格。");
    }
}
 
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
 
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.File;
 
public class XMLUtil
{
    public static Object getBean()
    {
        try
        {
            //创建DOM文档对象
            DocumentBuilderFactory dFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = dFactory.newDocumentBuilder();
            Document doc = builder.parse(new File("src/main/resources/config25.xml"));
 
            //获取包含类名的文本节点
            NodeList nl = doc.getElementsByTagName("className");
            Node classNode = nl.item(0).getFirstChild();
            String cName = classNode.getNodeValue();
 
            //通过类名生成实例对象并将其返回
            Class c = Class.forName(cName);
            Object obj = c.newInstance();
            return obj;
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return null;
        }
    }
}
 
 
/**
 * 测试类
 */
public class Client
{
    public static void main(String[] args)
    {
        //实例化商品
        Product b1 = new Book();
        Product b2 = new Book();
        Product a1 = new Apple();
 
        //实例化购物车
        BuyBasket basket = new BuyBasket();
        //添加商品
        basket.addProduct(b1);
        basket.addProduct(b2);
        basket.addProduct(a1);
 
        //实例化访问者
        Visitor visitor;
        //根据XML文件动态获取访问者
        visitor = (Visitor) XMLUtil.getBean();
        visitor.setName("张三");
        basket.accept(visitor);
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <className>Tutorial_25.Packager</className>
</config>