组合模式 读书笔记

允许你将对象组合成树形结构来表现“整体/部分”层次结构。组合能让客户以一致的方式处理个别对象以及对象组合。
创建一个树形结构，在同一个结构中处理嵌套菜单和菜单项组。通过将菜单和项放在相同的结构中，我们创建了一个“整体/部分”层次结构，即使由 菜单 和 菜单 项 组成 的 对象 树 。但是 可以 将 他视为 一个 整体，像是 一个 丰富的大菜单 。
1.我们应该努力让一个类只分配一个责任。
2.组合模式提供了一种结构，可同时包容个别对象和组合对象。
3。组合模式允许客户对个别对象和组合对象一视同仁。
4.组合结构内的任意对象称为组件，组件可以是组合，也可以是叶子节点。
5.在实现组合模式时，有许多设计上的 折中。你要根据需要平衡透明性和安全性。

package pattern; 
import java.util.ArrayList; 
import java.util.Iterator; 
import java.util.Stack; 
public class MenuTestDrive2 { 
public static void main(String[] args) { 
MenuComponent pancakeHouseMenu = new Menu("PANCAKE HOUSE MENU","Breakfast"); 
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,and sausage", true, 2.99)); 
pancakeHouseMenu.add(new MenuItem("BlueBerry Pancakes ", "Pancakes made with fresh blueberries", 
true, 3.49)); 
pancakeHouseMenu.add(new MenuItem("Waffles", 
"Waffles with your choice of blueberries or strawberries", 
true, 3.59)); 
MenuComponent dinerMenu = new Menu("DINER MENU","Lunch"); 
MenuComponent cafeMenu = new Menu("CAFE MENU","dINNER"); 
MenuComponent dessertMenu = new Menu("DESSERT MENU","Dessert of course!"); 
MenuComponent allMenus=new Menu("ALL MENUS","ALL menus combined"); 
allMenus.add(pancakeHouseMenu); 
allMenus.add(dinerMenu); 
allMenus.add(cafeMenu); 
cafeMenu.add(new MenuItem("Vegegie Burger and Air Fries", 
"Veggie burger on a whole wheat bun,lettuce,tomato,and fries", true, 
3.99)); 
dinerMenu.add(new MenuItem("Soup of the day", "A cup of the soup of the day,with a side salad", true, 
2.99)); 
dinerMenu.add(new MenuItem("Burrito", 
"A large burrito , with whole pinto beans,salsa,guacamole", true, 2.99)); 
dinerMenu.add(new MenuItem("Hotdog", 
"A hot dog, with saurkraut,relish,onions,topped with cheese", 
true, 2.99)); 
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 ice cream",true,1.59)); 

Waiter waitress = new Waiter(allMenus); 
waitress.printMenu(); 
} 
} 
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(){} 
public Iterator createIterator(){ 
throw new UnsupportedOperationException(); 
} 
} 
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 boolean isVegetarian() { 
return vegetarian; 
} 
public double getPrice() { 
return price; 
} 
public void print(){ 
System.out.print(" "+getName()); 
if(this.isVegetarian()){ 
System.out.println("(v)"); 
} 
System.out.println(","+getPrice()); 
System.out.println(" ---"+getDescription()); 
} 
public Iterator createIterator(){ 
return new NullIterator(); 
} 
} 
class Menu extends MenuComponent{ 

ArrayList menuComponents=new ArrayList(); 
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 iterator =(Iterator)menuComponents.iterator(); 
while(iterator.hasNext()){ 
MenuComponent menuComponent=(MenuComponent)iterator.next(); 
menuComponent.print(); 
} 
} 
public Iterator createIterator(){ 
return new CompositeIterator(menuComponents.iterator()); 
} 
} 
class CompositeIterator implements Iterator{ 
Stack stack=new Stack(); 
public CompositeIterator(Iterator iterator){ 
stack.push(iterator); 
} 
public Object next(){ 
if(hasNext()){ 
Iterator iterator=(Iterator)stack.peek(); 
MenuComponent component=(MenuComponent)iterator.next(); 
if(component instanceof Menu){ 
stack.push(component.createIterator()); 
} 
return component; 
}else{ 
return null; 
} 
} 
public boolean hasNext(){ 
if(stack.empty()){ 
return false; 
}else{ 
Iterator iterator =(Iterator)stack.peek(); 
if(!iterator.hasNext()){ 
stack.pop(); 
return hasNext(); 
}else{ 
return true; 
} 
} 
} 
public void remove(){ 
throw new UnsupportedOperationException(); 
} 
} 
class NullIterator implements Iterator{ 
public Object next(){ 
return null; 
} 
public boolean hasNext(){ 
return false; 
} 
public void remove(){ 
throw new UnsupportedOperationException(); 
} 
} 
class Waiter { 
MenuComponent allMenus; 
public Waiter(MenuComponent allMenus){ 
this.allMenus=allMenus; 
} 

public void printMenu() { 
this.allMenus.print(); 
} 
public void printVegetarianMenu(){ 
Iterator iterator=allMenus.createIterator(); 
System.out.println("\nVEGETARIAN MENU\n---"); 
while(iterator.hasNext()){ 
MenuComponent menuComponent=(MenuComponent)iterator.next(); 
try{ 
if(menuComponent.isVegetarian()){ 
menuComponent.print(); 
} 
} 
catch(UnsupportedOperationException e){} 
} 
} 
}