访问者模式（一）

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。

//Product.java
package test25;
public interface Product
{
    void accept(Visitor visitor);
}
//Apple.java
package test25;
public class Apple implements Product
{
  public void accept(Visitor visitor)
  {
      visitor.visit(this);
  }    
}
//Book.java
package test25;
public class Book implements Product
{
  public void accept(Visitor visitor)
  {
      visitor.visit(this);
  }    
}
//BuyBasket.java
package test25;
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 test25;
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 test25;
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 test25;
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 test25;
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);
}
//Client.java
package test25;
public class Client {
    public static void main(String[] args) {
        Product p1,p2;
        Visitor v1,v2,v3;
        p1=new Apple();
        p2=new Book();
        v1=new Saler();
        v1.setName("张三");
        v2=new Customer();
        v2.setName("李四");
        v3=new Packer();
        v3.setName("王五");
        BuyBasket basket = new BuyBasket();
        basket.addProduct(p1);
        basket.addProduct(p2);
        basket.accept(v1);
        basket.accept(v2);
        basket.accept(v3);
    }
}