软件设计25|访问者模式

 

一、Java版本

（1）效果如下：

（2）类图如下：

（3）目录如下：

（4）代码如下：

Apple.java

package visitor;

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

Book.java

package visitor;

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

BuyBasket.java

package visitor;

import java.util.ArrayList;
import java.util.Iterator;

@SuppressWarnings("rawtypes")
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);
        }
    }

    @SuppressWarnings("unchecked")
    public void addProduct(Product product) {
        list.add(product);
    }

    public void removeProduct(Product product) {
        list.remove(product);
    }
}

Client.java

package visitor;

public class Client {
    public static void main(String a[]) {
        Product b1 = new Book();
        Product b2 = new Book();
        Product a1 = new Apple();
        
        BuyBasket basket = new BuyBasket();
        basket.addProduct(b1);
        basket.addProduct(b2);
        basket.addProduct(a1);

        //创建顾客
        Customer customer = new Customer();
        customer.setName("张三");

        basket.accept(customer);
        
        System.out.println("--------");
        
        Saler saler=new Saler();
        saler.setName("李四");
        
        basket.accept(saler);
        
        System.out.println("--------");
        
        Packer packer=new Packer();
        packer.setName("王五");
        
        basket.accept(packer);
    }
}

Customer.java

package visitor;

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 visitor;

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

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

Product.java

package visitor;

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

Saler.java

package visitor;

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 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);
}

二、C++版本

（1）效果如下：

（2）类图如下：

（3）代码如下：

#include<iostream>
#include<List>
using namespace std;

//抽象访问者Visitor（访问者类）
class Apple;
class Book;
class Visitor {
public:
    void setName(string name) {
        this->name = name;
    }

    virtual void visit(Apple* apple) = 0;
    virtual void visit(Book* book) = 0;
protected:
    string name;
};

//具体访问者类Customer（顾客类） 
class Customer : public Visitor {
public:
    void visit(Apple* apple) {
        cout << "顾客" << name << "选苹果。" << endl;
    }

    void visit(Book* book) {
        cout << "顾客" << name << "买书。" << endl;
    }
};

//具体访问者类Saler（收银员类） 
class Saler : public Visitor {
public:
    void visit(Apple* apple) {
        cout << "收银员" << name << "给苹果过秤，然后计算价格。" << endl;
    }

    void visit(Book* book) {
        cout << "收银员" << name << "直接计算书的价格。" << endl;
    }
};

//抽象元素类Product（商品类）
class Product {
public:
    virtual void accept(Visitor* visitor) = 0;
};

//具体元素类Apple（苹果类） 
class Apple : public Product {
public:
    void accept(Visitor* visitor) {
        visitor->visit(this);
    }
};

//具体元素类Book（书籍类） 
class Book : public Product {
public:
    void accept(Visitor* visitor) {
        visitor->visit(this);
    }
};

//对象结构BuyBasket（购物车类）
class BuyBasket {
public:
    void accept(Visitor* visitor) {
        for (auto i : list) {
            i->accept(visitor);
        }
    }

    void addProduct(Product* product) {
        list.push_back(product);
    }

    void removeProduct(Product* product) {
        list.remove(product);
    }
private:
    list<Product*> list;
};

//具体访问者类Packer（打包员类） 
class Packer : public Visitor {
public:
    void visit(Apple* apple) {
        cout << "打包员" << name << "将苹果打包。" << endl;
    }

    void visit(Book* book) {
        cout << "打包员" << name << "将书打包。" << endl;
    }
};

//客户端测试 
int main(void)
{
    //创建商品 
    Book b1, b2;
    Apple a1;

    //创建购物车 
    BuyBasket basket;

    //购物车添加商品 
    basket.addProduct(&b1);
    basket.addProduct(&b2);
    basket.addProduct(&a1);

    //创建顾客 
    Customer customer;
    customer.setName("张三");

    //访问操作 
    basket.accept(&customer);

    //购物车移除商品 
    basket.removeProduct(&b2);

    cout << "-----------------" << endl;

    //创建收银员 
    Saler saler;
    saler.setName("李四");

    //访问操作 
    basket.accept(&saler);

    cout << "-----------------" << endl;

    //创建打包员
    Packer packer;
    packer.setName("王五");

    //访问操作 
    basket.accept(&packer);

    return 0;
}

参考链接：设计模式之访问者模式实例（c++）