访问者模式——java实现

问题描述：

 在我们课堂上的“购物车”的例子中，增加一个新的访问者：打包员，负责对购物车中货物装包。

Java源代码：

 

//Product.java
package shiyan25;

public interface Product
{
    void accept(Visitor visitor);
}

//Apple.java
package shiyan25;

public class Apple implements Product
{
  public void accept(Visitor visitor)
  {
      visitor.visit(this);
  }    
}
//Book.java
package shiyan25;
public class Book implements Product
{
  public void accept(Visitor visitor)
  {
      visitor.visit(this);
  }    
}
//BuyBasket.java
package shiyan25;

import java.util.*;

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);    
        }
    }
    
    public void addProduct(Product product)
    {
        list.add(product);
    }
    
    public void removeProduct(Product product)
    {
        list.remove(product);
    }
}
//Customer.java
package shiyan25;

public class Customer extends Visitor
{
    public void visit(Apple apple)
    {
        System.out.println("顾客" + name + "选苹果。");
    }
    
    public void visit(Book book)
    {
        System.out.println("顾客" + name + "买书。");
    }
}
//Packer.java
package shiyan25;

public class Packer extends Visitor {

    @Override
    public void visit(Apple apple) {
        // TODO 自动生成的方法存根
        System.out.println("打包员" + name + "给购物车中的苹果打包。");
    }

    @Override
    public void visit(Book book) {
        // TODO 自动生成的方法存根
        System.out.println("打包员" + name + "给购物车中的书本打包。");
    }

}
//Saler.java
package shiyan25;

public class Saler extends Visitor
{
    public void visit(Apple apple)
    {
        System.out.println("收银员" + name + "给苹果过秤，然后计算其价格。");
    }
    
    public void visit(Book book)
    {
        System.out.println("收银员" + name + "直接计算书的价格。");
    }
}
//Visitor.java
package shiyan25;

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);
}
//XMLUtil.java
package shiyan25;

import javax.xml.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.SAXException;
import java.io.*;
public class XMLUtil
{
//该方法用于从XML配置文件中提取具体类类名，并返回一个实例对象
    public static Object getBean()
    {
        try
        {
            //创建文档对象
            DocumentBuilderFactory dFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = dFactory.newDocumentBuilder();
            Document doc;                            
            doc = builder.parse(new File("src/shiyan25/config.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("shiyan25."+cName);
              Object obj=c.newInstance();
            return obj;
           }   
               catch(Exception e)
               {
                   e.printStackTrace();
                   return null;
               }
        }
    public static Object getBean2()
    {
        try
        {
            //创建文档对象
            DocumentBuilderFactory dFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = dFactory.newDocumentBuilder();
            Document doc;                            
            doc = builder.parse(new File("src/shiyan25/config_packer.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("shiyan25."+cName);
              Object obj=c.newInstance();
            return obj;
           }   
               catch(Exception e)
               {
                   e.printStackTrace();
                   return null;
               }
        }
}

运行结果：