软件设计访问者模式

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

Java

package rjsj.no25;

public class Client {

    public static void main(String[] args) {
        Product b1 = new Book();
        Product a1 = new Apple();
        Visitor visitor;
        
        BuyBasket basket = new BuyBasket();
        basket.addProduct(b1);
        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);
    }

}

package rjsj.no25;

public class Customer extends Visitor{

    @Override
    public void visit(Apple apple) {
        System.out.println("顾客->" + name + "买苹果");
    }

    @Override
    public void visit(Book book) {
        System.out.println("顾客->" + name + "买书");
    }
    
}

package rjsj.no25;

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");
    }
}

package rjsj.no25;

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

package rjsj.no25;

public class Saler extends Visitor{

    @Override
    public void visit(Apple apple) {
        System.out.println("收银员->" + name + "计算苹果价格");
    }

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

}

package rjsj.no25;

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);
}

package rjsj.no25;

public class Apple implements Product{

    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }
}

package rjsj.no25;

public class Book implements Product{

    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }
}

package rjsj.no25;

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

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);
    }
}

C++

#include<iostream>
#include <vector>
#include <algorithm>
using namespace std;
class Apple;
class Book;
class Visitor {
protected:
    string name;
public:
    void setName(string name) {
        this->name=name;
    }
    virtual void visit(Apple *apple)=0;
    virtual void visit(Book *book)=0;
};

class Customer :public Visitor{
public:
    void visit(Apple *apple) {
        cout<<"顾客->"<<name<<"买苹果"<<endl;
    }
    void visit(Book *book) {
        cout<<"顾客->"<<name<<"买书"<<endl;
    }
};

class Packer: public Visitor{
public:
    void visit(Apple *apple) {
        cout<<"打包员->"<<name<<"给苹果打包"<<endl;
    }
    void visit(Book *book) {
        cout<<"打包员->"<<name<<"给书打包"<<endl;
    }
};

class Saler:public Visitor{
public:
    void visit(Apple *apple) {
        cout<<"收银员->"<<name<<"计算苹果价格"<<endl;
    }
    void visit(Book *book) {
        cout<<"收银员->"<<name<<"计算书的价格"<<endl;
    }
};

class Product {
public:
    virtual void accept(Visitor *visitor)=0;
};

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 BuyBasket {
private:
    vector <Product *> products;
public:
    void accept(Visitor *visitor) {
        vector <Product *>::iterator iProduct = products.begin();
         while(iProduct != products.end())
         {
              (*iProduct)->accept(visitor);
              iProduct++;
         }
    }
    void addProduct(Product *product) {
        products.push_back(product);
    }
    void removeProduct(Product *product) {
        vector<Product*>::iterator product_rm = find(products.begin(), products.end(), product);
        products.erase(product_rm);
    }
};

int main(){
    Product *b1=new Book();
    Product *a1=new Apple();
    Product *a2=new Apple();
    Visitor *visitor;
    BuyBasket *basket=new BuyBasket();
    basket->addProduct(b1);
    basket->addProduct(a1);
    basket->addProduct(a2);

    visitor=new Customer();
    visitor->setName("张三");
    basket->accept(visitor);
    cout<<"########################################"<<endl;
    visitor=new Packer();
    visitor->setName("李四");
    basket->accept(visitor);
    cout<<"########################################"<<endl;
    visitor=new Saler();
    visitor->setName("王五");
    basket->accept(visitor);
}

运行结果