访问者模式

实验 25：访问者模式

本次实验属于模仿型实验，通过本次实验学生将掌握以下内容：

1、理解访问者模式的动机，掌握该模式的结构；

2、能够利用访问者模式法解决实际问题。

[实验任务一]：打包员

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。

类图

 

源代码

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

    @Override
    public void accept(Visitor visitor) {
        // TODO Auto-generated method stub
        visitor.visit(this);
    }
    
}
public class Book implements Product{

    @Override
    public void accept(Visitor visitor) {
        // TODO Auto-generated method stub
        visitor.visit(this);
    }

}
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);
    }
}
public class Customer extends Visitor{

    @Override
    public void visit(Apple apple) {
        // TODO Auto-generated method stub
        System.out.println("顾客"+name+"选苹果。");
    }

    @Override
    public void visit(Book book) {
        // TODO Auto-generated method stub
        System.out.println("顾客"+name+"买书。");
    }
    
}
public class Packer extends Visitor{

    @Override
    public void visit(Apple apple) {
        // TODO Auto-generated method stub
        System.out.println("打包员"+name+"给苹果打包。");
    }

    @Override
    public void visit(Book book) {
        // TODO Auto-generated method stub
        System.out.println("打包员"+name+"给书打包。");
    }

}
public class Saler extends Visitor{

    @Override
    public void visit(Apple apple) {
        // TODO Auto-generated method stub
        System.out.println("收银员"+name+"给苹果过秤，然后计算其价格");
    }

    @Override
    public void visit(Book book) {
        // TODO Auto-generated method stub
        System.out.println("收银员"+name+"直接计算书的价格。");
    }

}
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);
}
public class Client {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Product b1=new Book();
        Product b2=new Book();
        Product a1=new Apple();
        Visitor visitor;
        
        BuyBasket basket=new BuyBasket();
        basket.addProduct(b1);
        basket.addProduct(b2);
        basket.addProduct(a1);
        
        visitor=new Customer();
        visitor.setName("张三");
        basket.accept(visitor);
        System.out.println("----------------------------");
        visitor=new Packer();
        visitor.setName("李四");
        basket.accept(visitor);
        System.out.println("----------------------------");
        visitor=new Saler();
        visitor.setName("王五");
        basket.accept(visitor);
    }

}