迭代器模式(iterator pattern) 详细解释
本文地址: http://blog.csdn.net/caroline_wendy
迭代器模式(iterator pattern) : 提供一种方法顺序訪问一个聚合对象中的各个元素, 而又不暴露其内部的表示;
建立迭代器接口(iterator interface), 包括hasNext()方法和next()方法;
不同聚合对象的详细的迭代器(concrete iterator), 继承(implements)迭代器接口(iterator interface), 实现hasNext()方法和next()方法;
详细聚合对象(concrete aggregate), 提供创建迭代器的方法(createIterator).
通过调用聚合对象的迭代器, 就可以使用迭代器, 统一输出接口.
面向对象设计原则:
一个类应该仅仅有一个引起变化的原因.
即一个类应该仅仅有一个责任, 即高内聚.
详细方法:
1. 菜单项, ArrayList和数组的基本元素.
/** * @time 2014年6月20日 */package iterator;/** * @author C.L.Wang * */public class MenuItem { String name; String description; boolean vegetarian; //是否是素食 double price; /** * */ public MenuItem(String name, String description, boolean vegetarian, double price) { // TODO Auto-generated constructor stub 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; } } 2. 详细的聚合对象(concrete aggregate), 包括创建迭代器的方法(createIterator).
/** * @time 2014年6月26日 */package iterator;/** * @author C.L.Wang * */public class DinerMenu { static final int MAX_ITEMS = 6; int numberOfItems = 0; MenuItem[] menuItems; /** * */ public DinerMenu() { // TODO Auto-generated constructor stub 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 the whole wheat", false, 2.99); addItem("Soup of the day", "Soup of the day, with a side of potato salad", false, 3.29); addItem("Hotdog", "A hot dog, with saurkraut, relish, onions, topped 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[numberOfItems] = menuItem; ++numberOfItems; } } public Iterator createIterator() { return new DinerMenuIterator(menuItems); } }/** * @time 2014年6月20日 */package iterator;import java.util.ArrayList;/** * @author C.L.Wang * */public class PancakeHouseMenu { ArrayList 3. 迭代器接口(iterator interface), 包括hasNext()方法和next()方法. /** * @time 2014年6月27日 */package iterator;/** * @author C.L.Wang * */public interface Iterator { boolean hasNext(); Object next(); } 4. 聚合对象的 详细的迭代器(concrete iterator) , 继承(implements) 迭代器接口(iterator interface), 实现hasNext()方法和next()方法; /** * @time 2014年6月27日 */package iterator;/** * @author C.L.Wang * */public class DinerMenuIterator implements Iterator { MenuItem[] items; int position = 0; /** * */ public DinerMenuIterator(MenuItem[] items) { // TODO Auto-generated constructor stub this.items = items; } /* (non-Javadoc) * @see iterator.Iterator#hasNext() */ @Override public boolean hasNext() { // TODO Auto-generated method stub if (position >= items.length || items[position] == null) { return false; } return true; } /* (non-Javadoc) * @see iterator.Iterator#next() */ @Override public Object next() { // TODO Auto-generated method stub MenuItem menuItem = items[position]; ++position; return menuItem; }}/** * @time 2014年6月27日 */package iterator;import java.util.ArrayList;/** * @author C.L.Wang * */public class PancakeHouseMenuIterator implements Iterator { ArrayList 5. 客户类使用详细聚合类(concrete aggregate)的迭代器(iterator). /** * @time 2014年6月27日 */package iterator;/** * @author C.L.Wang * */public class Waitress { PancakeHouseMenu pancakeHouseMenu; DinerMenu dinerMenu; /** * */ public Waitress(PancakeHouseMenu pancakeHouseMenu, DinerMenu dinerMenu) { // TODO Auto-generated constructor stub 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.print(menuItem.getName() + ": "); System.out.print(menuItem.getPrice() + " -- "); System.out.println(menuItem.getDescription()); } }} 6. 測试代码: /** * @time 2014年6月27日 */package iterator;/** * @author C.L.Wang * */public class MenuTestDrive { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu(); DinerMenu dinerMenu = new DinerMenu(); Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu); waitress.printMenu(); }} 7. 输出: MENU----BREAKFASTK&B's Pancake Breakfast: 2.99 -- Pancakes with scrambled eggs, and toastRegular Pancake Breakfast: 2.99 -- Pancakes with fried eggs, sausageBlueberry Pancakes: 3.49 -- Pancakes made with fresh blueberriesWaffles: 3.59 -- Waffles, with your choice of blueberries or strawberriesLUNCHVegetarian BLT: 2.99 -- (Fakin') Bacon with lettuce & tomato on whole wheatBLT: 2.99 -- Bacon with lettuce & tomato on the whole wheatSoup of the day: 3.29 -- Soup of the day, with a side of potato saladHotdog: 3.05 -- A hot dog, with saurkraut, relish, onions, topped with cheese
