Iterator Pattern

今天抽空看了Iterator Pattern，對programming to interface有了更多的理解，design pattern真是一本好書，完全站在了讀者的角度，用問題的方式一個個解決，讓人有痛快淋漓的感覺。書中例子我實現了下如下是代碼，csdn中必須在網頁中才能插入代碼：

package iterator; import java.util.Iterator; public interface Menu { public Iterator createIterator(); }  

package iterator; import java.util.Iterator;; public class DinerMenu implements Menu{ static final int MAX_ITEMS = 6; int numberOfItems = 0; MenuItem[] menuItems; public DinerMenu(){ menuItems = new MenuItem[MAX_ITEMS]; addItem("Vegetarian BLT", "(Fakin') Bacon with lettuce & tomato on whole wheat", true, 2.99); addItem("BLT", "Bacon with lettuce & tomato on whole wheat", false, 2.99); addItem("Soup of the day", "Soup of the day, with a side of potato salad,", false, 2.39); addItem("Hotdog", "a hot dog, with saurkraut,relish ,onions, toppe with cheese", false, 3.05); } public void addItem(String name,String description, boolean vegetarian,double price){ MenuItem menuItem = new MenuItem(name,description,vegetarian,price); if (numberOfItems >= MAX_ITEMS){ System.err.println("Sorry menu is full!Can't add item to menu"); } else{ menuItems[this.numberOfItems] = menuItem; numberOfItems++; } } public Iterator createIterator(){ return new DinerMenuIterator(menuItems); } }  

package iterator; import java.util.*; public class PancakeHouseMenu implements Menu{ ArrayList menuItems; public PancakeHouseMenu(){ menuItems = new ArrayList(); addItem("K&B's pancake Breakfast", "Pancakes with scrambled eggs, and totst", true,2.99); addItem("Regular Pancake Breakfast", "Pancakes with fried eggs, sausage", false, 2.99); addItem("Blueberry Pancakes", "Pancakses made with fresh blueberries", true, 3.49); addItem("Waffles", "Waffles, with your chioce of blueberries or strawberries", true, 3.59); } public void addItem(String name,String description, boolean vegetarian,double price){ MenuItem menuItem = new MenuItem(name,description,vegetarian,price); menuItems.add(menuItem); } public Iterator createIterator(){ return menuItems.iterator(); } }  

 

package iterator; public class MenuItem { 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 name; } public double getPrice(){ return price; } public boolean isVegetarian(){ return vegetarian; } }  

 

package iterator; import java.util.Iterator; public class DinerMenuIterator implements Iterator{ MenuItem[] items; int position = 0; public DinerMenuIterator(MenuItem[] items){ this.items = items; } public boolean hasNext() { if (position >= items.length || null == items[position]){ return false; } else{ return true; } } public Object next() { MenuItem menuItem = items[position++]; return menuItem; } public void remove() { if (position <= 0){ throw new IllegalStateException ("You can't remove an item until you've done at least on next()"); } } }  

 

package iterator; import java.util.Iterator; public class Waitress { Menu pancakeHouseMenu; Menu dinerMenu; public Waitress(Menu pancakeHouseMenu,Menu dinerMenu){ this.pancakeHouseMenu = pancakeHouseMenu; this.dinerMenu = dinerMenu; } public void printMenu(){ Iterator pancakeIterator = pancakeHouseMenu.createIterator(); Iterator dinerIterator = dinerMenu.createIterator(); System.out.println("MENU/n---/nBREAKFAST"); printMenu(pancakeIterator); System.out.println("/nLUNCH"); printMenu(dinerIterator); } private void printMenu(Iterator iterator){ while (iterator.hasNext()){ MenuItem menuItem = (MenuItem)iterator.next(); System.out.println(menuItem.getName() + "."); System.out.println(menuItem.getPrice() + "--"); System.out.println(menuItem.getDescription()); } } }  

 

package iterator; public class MenuTestDrive { public static void main(String[] args){ PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu(); DinerMenu dinerMenu = new DinerMenu(); Waitress waitress = new Waitress(pancakeHouseMenu,dinerMenu); waitress.printMenu(); } }  

Iterator可以完全不用考慮底層的實現而讀取數據，不管是什麼類型，這樣就可以共用一個printMenu的方法，每一個菜單都是menu的實現，在Waitress中就不用考慮Menu的類型，抽象的太好了。一定要把此書精讀。