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<MenuItem> menuItems; /**
*
*/
public PancakeHouseMenu() {
// TODO Auto-generated constructor stub
menuItems = new ArrayList<MenuItem>(); addItem("K&B's Pancake Breakfast",
"Pancakes with scrambled eggs, and toast", true, 2.99); addItem("Regular Pancake Breakfast",
"Pancakes with fried eggs, sausage", false, 2.99); addItem("Blueberry Pancakes",
"Pancakes made with fresh blueberries", true, 3.49); addItem("Waffles",
"Waffles, with your choice 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 new PancakeHouseMenuIterator(menuItems);
} }

3. 迭代器接口(iterator interface), 包括hasNext()方法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<MenuItem> menuItems;
int position; /**
*
*/
public PancakeHouseMenuIterator(ArrayList<MenuItem> menuItems) {
// TODO Auto-generated constructor stub
this.menuItems = menuItems;
} /* (non-Javadoc)
* @see iterator.Iterator#hasNext()
*/
@Override
public boolean hasNext() {
// TODO Auto-generated method stub
if (position >= menuItems.size() || menuItems.get(position) == null) {
return false;
} return true;
} /* (non-Javadoc)
* @see iterator.Iterator#next()
*/
@Override
public Object next() {
// TODO Auto-generated method stub MenuItem menuItem = menuItems.get(position);
++position; return menuItem;
} }

5. 客户类使用详细聚合类(concrete aggregate)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
----
BREAKFAST
K&B's Pancake Breakfast: 2.99 -- Pancakes with scrambled eggs, and toast
Regular Pancake Breakfast: 2.99 -- Pancakes with fried eggs, sausage
Blueberry Pancakes: 3.49 -- Pancakes made with fresh blueberries
Waffles: 3.59 -- Waffles, with your choice of blueberries or strawberries LUNCH
Vegetarian BLT: 2.99 -- (Fakin') Bacon with lettuce & tomato on whole wheat
BLT: 2.99 -- Bacon with lettuce & tomato on the whole wheat
Soup of the day: 3.29 -- Soup of the day, with a side of potato salad
Hotdog: 3.05 -- A hot dog, with saurkraut, relish, onions, topped with cheese