设计模式——迭代器与组合模式（二）

11（二）.

前一篇文章是讲迭代器模式的。

现在有一个新需求：要在餐厅菜单中添加一个甜点菜单，示意图如下：



这样的话要如何处理？

此时可用组和模式。

OO模式： 组合模式——允许你将对象组成树形结构来表现“整体/部分”的层次结构。组合能让客户一一直的方式处理个别对象和对象组合。

实现菜单组件：

public abstract class MenuComponent {

public void add(MenuComponent menuComponent) {
throw new UnsupportedOperationException();
}
public void remove(MenuComponent menuComponent) {
throw new UnsupportedOperationException();
}
public MenuComponent getChild(int i) {
throw new UnsupportedOperationException();
}

public String getName() {
throw new UnsupportedOperationException();
}
public String getDescription() {
throw new UnsupportedOperationException();
}
public double getPrice() {
throw new UnsupportedOperationException();
}
public boolean isVegetarian() {
throw new UnsupportedOperationException();
}

public void print() {
throw new UnsupportedOperationException();
}
}

实现菜单项：
public class MenuItem extends MenuComponent {
String name;
String description;
boolean vegetarian;
double price;

public MenuItem(String name,
String description,
boolean vegetarian,
double price)
{
this.name = name;
this.description = description;
this.vegetarian = vegetarian;
this.price = price;
}

public String getName() {
return name;
}

public String getDescription() {
return description;
}

public double getPrice() {
return price;
}

public boolean isVegetarian() {
return vegetarian;
}

public void print() {
System.out.print(" " + getName());
if (isVegetarian()) {
System.out.print("(v)");
}
System.out.println(", " + getPrice());
System.out.println(" -- " + getDescription());
}
}

实现组合菜单：
import java.util.Iterator;
import java.util.ArrayList;

public class Menu extends MenuComponent {
ArrayList<MenuComponent> menuComponents = new ArrayList<MenuComponent>();
String name;
String description;

public Menu(String name, String description) {
this.name = name;
this.description = description;
}

public void add(MenuComponent menuComponent) {
menuComponents.add(menuComponent);
}

public void remove(MenuComponent menuComponent) {
menuComponents.remove(menuComponent);
}

public MenuComponent getChild(int i) {
return (MenuComponent)menuComponents.get(i);
}

public String getName() {
return name;
}

public String getDescription() {
return description;
}

public void print() {
System.out.print("\n" + getName());
System.out.println(", " + getDescription());
System.out.println("---------------------");

Iterator<MenuComponent> iterator = menuComponents.iterator();
while (iterator.hasNext()) {
MenuComponent menuComponent =
(MenuComponent)iterator.next();
menuComponent.print();
}
}
}
更新女招待的代码：

public class Waitress {
MenuComponent allMenus;

public Waitress(MenuComponent allMenus) {
this.allMenus = allMenus;
}

public void printMenu() {
allMenus.print();
}
}
测试代码：

public class MenuTestDrive {
public static void main(String args[]) {
MenuComponent pancakeHouseMenu =
new Menu("PANCAKE HOUSE MENU", "Breakfast");
MenuComponent dinerMenu =
new Menu("DINER MENU", "Lunch");
MenuComponent cafeMenu =
new Menu("CAFE MENU", "Dinner");
MenuComponent dessertMenu =
new Menu("DESSERT MENU", "Dessert of course!");
MenuComponent coffeeMenu = new Menu("COFFEE MENU", "Stuff to go with your afternoon coffee");

MenuComponent allMenus = new Menu("ALL MENUS", "All menus combined");

allMenus.add(pancakeHouseMenu);
allMenus.add(dinerMenu);
allMenus.add(cafeMenu);

pancakeHouseMenu.add(new MenuItem(
"K&B's Pancake Breakfast",
"Pancakes with scrambled eggs, and toast",
true,
2.99));
pancakeHouseMenu.add(new MenuItem(
"Regular Pancake Breakfast",
"Pancakes with fried eggs, sausage",
false,
2.99));
pancakeHouseMenu.add(new MenuItem(
"Blueberry Pancakes",
"Pancakes made with fresh blueberries, and blueberry syrup",
true,
3.49));
pancakeHouseMenu.add(new MenuItem(
"Waffles",
"Waffles, with your choice of blueberries or strawberries",
true,
3.59));

dinerMenu.add(new MenuItem(
"Vegetarian BLT",
"(Fakin') Bacon with lettuce & tomato on whole wheat",
true,
2.99));
dinerMenu.add(new MenuItem(
"BLT",
"Bacon with lettuce & tomato on whole wheat",
false,
2.99));
dinerMenu.add(new MenuItem(
"Soup of the day",
"A bowl of the soup of the day, with a side of potato salad",
false,
3.29));
diner
4000
Menu.add(new MenuItem(
"Hotdog",
"A hot dog, with saurkraut, relish, onions, topped with cheese",
false,
3.05));
dinerMenu.add(new MenuItem(
"Steamed Veggies and Brown Rice",
"Steamed vegetables over brown rice",
true,
3.99));

dinerMenu.add(new MenuItem(
"Pasta",
"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
true,
3.89));

dinerMenu.add(dessertMenu);

dessertMenu.add(new MenuItem(
"Apple Pie",
"Apple pie with a flakey crust, topped with vanilla icecream",
true,
1.59));

dessertMenu.add(new MenuItem(
"Cheesecake",
"Creamy New York cheesecake, with a chocolate graham crust",
true,
1.99));
dessertMenu.add(new MenuItem(
"Sorbet",
"A scoop of raspberry and a scoop of lime",
true,
1.89));

cafeMenu.add(new MenuItem(
"Veggie Burger and Air Fries",
"Veggie burger on a whole wheat bun, lettuce, tomato, and fries",
true,
3.99));
cafeMenu.add(new MenuItem(
"Soup of the day",
"A cup of the soup of the day, with a side salad",
false,
3.69));
cafeMenu.add(new MenuItem(
"Burrito",
"A large burrito, with whole pinto beans, salsa, guacamole",
true,
4.29));

cafeMenu.add(coffeeMenu);

coffeeMenu.add(new MenuItem(
"Coffee Cake",
"Crumbly cake topped with cinnamon and walnuts",
true,
1.59));
coffeeMenu.add(new MenuItem(
"Bagel",
"Flavors include sesame, poppyseed, cinnamon raisin, pumpkin",
false,
0.69));
coffeeMenu.add(new MenuItem(
"Biscotti",
"Three almond or hazelnut biscotti cookies",
true,
0.89));

Waitress waitress = new Waitress(allMenus);

waitress.printMenu();
}
}