每日总结11.30

访问者模式
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：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。

Client.java
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);
    }

}

Customer.java
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");
    }
    
}

Packer.java
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");
    }
}

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

Saler.java
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");
    }

}

Visitor.java
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);
}

Apple.java
public class Apple implements Product{

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

Book.java
public class Book implements Product{

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

BuyBasket.java
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);
    }
}