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);
}
}
