迭代器模式(iterator pattern) Java 迭代器(Iterator) 详解
本文地址: http://blog.csdn.net/caroline_wendy
参考迭代器模式(iterator pattern): http://blog.csdn.net/caroline_wendy/article/details/35254643
Java的标准库(util)中包含迭代器接口(iterator interface), import java.util.Iterator;
继承(implements)迭代器接口(Iterator)需要重写(override)三个函数: hasNext(), next()和remove();
Java的聚合类型, 如ArrayList包含迭代器.
但是数组类型, 需要重写相应的迭代器(iterator).
具体方法:
1. ArrayList类型, 包含迭代器的方法, 可以直接返回.
/**
* @time 2014年6月20日
*/
package iterator;
import java.util.ArrayList;
import java.util.Iterator;
/**
* @author C.L.Wang
*
*/
public class PancakeHouseMenu implements Menu {
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<MenuItem> createIterator() {
return menuItems.iterator();
}
}
2. 数组类型, 创建相应的迭代器类, 继承(implements)迭代器(Iterator), 重写迭代器的方法.
/**
* @time 2014年6月26日
*/
package iterator;
import java.util.Iterator;
/**
* @author C.L.Wang
*
*/
public class DinerMenu implements Menu {
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<MenuItem> createIterator() {
return new DinerMenuIterator(menuItems);
}
}
/**
* @time 2014年6月27日
*/
package iterator;
import java.util.Iterator;
/**
* @author C.L.Wang
*
*/
public class DinerMenuIterator implements Iterator<MenuItem> {
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 MenuItem next() {
// TODO Auto-generated method stub
MenuItem menuItem = items[position];
++position;
return menuItem;
}
@Override
public void remove() {
if (position <= 0) {
throw new IllegalStateException
("You can‘t remove an item until you‘ve done at least one next()");
}
if (items[position-1] != null) {
for (int i=position-1; i<(items.length-1); ++i) {
items[i] = items[i+1];
}
items[items.length-1] = null;
}
}
}
3. 菜单接口(interface), 包含创建迭代器(createIterator)的方法.
/**
* @time 2014年6月27日
*/
package iterator;
import java.util.Iterator;
/**
* @author C.L.Wang
*
*/
public interface Menu {
public Iterator<MenuItem> createIterator();
}
4. 具体的菜单项, 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;
}
}
5. 客户类(client), 调用迭代器(iterator)方法.
/**
* @time 2014年6月27日
*/
package iterator;
import java.util.Iterator;
/**
* @author C.L.Wang
*
*/
public class Waitress {
Menu pancakeHouseMenu;
Menu dinerMenu;
/**
*
*/
public Waitress(Menu pancakeHouseMenu, Menu dinerMenu) {
// TODO Auto-generated constructor stub
this.pancakeHouseMenu = pancakeHouseMenu;
this.dinerMenu = dinerMenu;
}
public void printMenu() {
Iterator<MenuItem> pancakeIterator = pancakeHouseMenu.createIterator();
Iterator<MenuItem> dinerIterator = dinerMenu.createIterator();
System.out.println("MENU\n----\nBREAKFAST");
printMenu(pancakeIterator);
System.out.println("\nLUNCH");
printMenu(dinerIterator);
}
private void printMenu(Iterator<MenuItem> 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. 测试:
/**
* @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
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