访问者模式--Java实现

具体代码

//Visitor.java
package org.example.test023;

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);
}

//Customer.java
package org.example.test023;

public class Customer extends Visitor {
    @Override
        public void visit(Apple apple) {
        System.out.println("顾客" + name + "苹果");
    }

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

//Saler.java
package org.example.test023;

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");
    }
}

//Packager.java
package org.example.test023;

public class Packager 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 + "给书籍打包");
    }
}

//Product.java
package org.example.test023;

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

//Apple.java
package org.example.test023;

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

//Book.java
package org.example.test023;

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

//BuyBasket.java
package org.example.test023;

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);
        }
    }

    //加入购物车
    public void addProduct(Product product) {
        list.add(product);
    }

    //移出购物车
    public void removeProduct(Product product) {
        list.remove(product);
    }
}

//Client.java
package org.example.test023;

public class Client {
    public static void main(String[] args) {
        Product b1 = new Book();
        Product b2 = new Book();
        Product b3 = new Apple();

        Visitor visitor;

        BuyBasket buyBasket = new BuyBasket();

        buyBasket.addProduct(b1);
        buyBasket.addProduct(b2);
        buyBasket.addProduct(b3);

        //设置顾客为张三
        visitor = new Customer();
        visitor.setName("张三");
        buyBasket.accept(visitor);

        //设置收银员为李四
        visitor = new Saler();
        visitor.setName("李四");
        buyBasket.accept(visitor);

        //设置打包员为王五
        visitor = new Packager();
        visitor.setName("王五");
        buyBasket.accept(visitor);
    }
}

运行结果