设计模式之访问者模式

题目

[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：

类图

Java

Product

package com.gazikel;

public interface Product {

    void accept(Visitor visitor);
}

Product实现类

Apple

package com.gazikel;

public class Apple implements Product {
    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }
}

Book

package com.gazikel;

public class Book implements Product {
    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }
}

Visitor

package com.gazikel;



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);
}

Visitor实现类

Customer

package com.gazikel;

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");
    }
}

Packer

package com.gazikel;

public class Packer extends Visitor {
    @Override
    public void visit(Apple apple) {
        System.out.println("打包员" + name + "给苹果打包");
    }

    @Override
    public void visit(Book book) {
        System.out.println("打包员" + name + "给书打包");
    }
}

Saler

package com.gazikel;

public class Saler extends Visitor {
    @Override
    public void visit(Apple apple) {
        System.out.println("收银员" + name + "给苹果过秤，然后计算其价格");
    }

    @Override
    public void visit(Book book) {
        System.out.println("收银员" + name + "直接计算书的价格");

    }
}

BuyBasket

package com.gazikel;

import java.util.ArrayList;
import java.util.List;

public class BuyBasket {

    private List<Product> products = new ArrayList();

    public void accept(Visitor visitor) {
        for (Product product : products) {
            product.accept(visitor);
        }
    }

    public void addProduct(Product p) {
        products.add(p);
    }

    public void removeProduct(Product p) {
        products.remove(p);
    }
}

Client

package com.gazikel;

public class Client {

    public static void main(String[] args) {
        BuyBasket buyBasket = new BuyBasket();

        buyBasket.addProduct(new Apple());
        buyBasket.addProduct(new Book());

        Visitor saler = new Saler();
        saler.setName("张三");
        System.out.println("----收银员----");
        buyBasket.accept(saler);

        Visitor packer = new Packer();
        packer.setName("李四");
        System.out.println("----打包员----");
        buyBasket.accept(packer);

        Visitor customer = new Customer();
        customer.setName("王五");
        System.out.println("----顾客----");
        buyBasket.accept(customer);
    }
}

C++

main.cpp

#include <iostream>
#include <string>
#include <list>
using namespace std;

class Product;
class Book;
class Apple;

class Visitor
{
protected:
	string name;
public:
	void SetName(string name) {
		this->name = name;
	}
	virtual void Visit(Apple *apple) {};
	virtual void Visit(Book *book) {};
};


class Product
{
public:
	// Methods
	virtual void Accept(Visitor *visitor) {};
};


// "ConcreteElement"
class Apple : public Product {
public:

	void Accept(Visitor *visitor) {
		visitor->Visit(this);
	}
};

class Book :public Product {
public:
	void Accept(Visitor* visitor) {
		visitor->Visit(this);
	}
};

class Customer : public Visitor {
public:
	void Visit(Book *book) {
		cout << "顾客" << name << "买书" << endl;
	}

	void Visit(Apple *apple) {
		cout << "顾客" << name << "选苹果" << endl;
	}
};

class Saler : public Visitor {
public:
	void Visit(Book *book) {
		cout << "收银员" << name << "直接计算书的价格" << endl;
	}

	void Visit(Apple *apple) {
		cout << "收银员" << name << "给苹果过秤，然后计算其价格" << endl;
	}
};

class Packer : public Visitor {
public:
	void Visit(Book *book) {
		cout << "打包员" << name << "给书打包" << endl;
	}

	void Visit(Apple *apple) {
		cout << "打包员" << name << "给苹果打包" << endl;
	}
};


// "ObjectStructure"
class BuyBasket
{
private:
	list<Product*> products;

public:

	void Attach(Product *product)
	{
		products.push_back(product);
	}

	void Detach(Product *product)
	{
		products.remove(product);
	}

	void Accept(Visitor *visitor)
	{
		for (std::list<Product*>::iterator it = products.begin(); it != products.end(); ++it)
			(*it)->Accept(visitor);
	}
};

int main()
{
	BuyBasket *buybasket = new BuyBasket();

	Product* apple = new Apple();
	Product* book = new Book();

	buybasket->Attach(apple);
	buybasket->Attach(book);

	Customer *customer = new Customer();
	customer->SetName("张三");
	Saler* saler = new Saler();
	saler->SetName("李四");
	Packer* packer = new Packer();
	packer->SetName("王五");

	// Employees are visited
	cout << "----customer----" << endl;
	buybasket->Accept(customer);

	cout << "----saler----" << endl;
	buybasket->Accept(saler);

	cout << "----packer----" << endl;
	buybasket->Accept(packer);
}