Iterator patten 读书笔记

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提供 一种方法 顺序访问 一个聚和 对象中的各个元素，而又不暴露其内部的表示或实现。
迭代器模式让我们能游走于聚合内的每一个元素，而又不暴露其内部的表示。把游走的任务放在迭代器上，而不是聚合上。这样简化了聚合的接口和实现，也让责任各得其所。
1.迭代器允许访问聚合的元素，而不需要暴露它的内部结构。
2.迭代器将遍历聚合的工作封装进一个对象中。
3.当使用迭代器的时候，我们依赖聚合提供遍历。
4.迭代器提供了一个通用的接口，让我们遍历聚合项，当我们编码使用聚合的项时，就可以使用多太机制。

package pattern;
import java.util.ArrayList;
import java.util.Calendar;
import com.sun.org.apache.xalan.internal.xsltc.runtime.Hashtable;
public class MenuTestDrive {
 public static void main(String[] args) {
  PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
  DinerMenu dinerMenu = new DinerMenu();
  CafeMenu cafeMenu = new CafeMenu();
  Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu,cafeMenu);
  waitress.printMenu();
 }
}
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 description;
 }
 public boolean isVegetarian() {
  return vegetarian;
 }
 public double getPrice() {
  return price;
 }
}
interface Menu{
 public Iterator creatIterator();
}
class PancakeHouseMenu implements Menu {
 ArrayList menuItems=new ArrayList();
 public PancakeHouseMenu() {
  menuItems = new ArrayList();
  addItem("K&B'S Pancake Breakfast",
    "Pancakes with scrambled eggs,and toast", true, 2.99);
  addItem("Regular Pancake Breakfast",
    "Pancakes with fried eggs,and sausage", true, 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 creatIterator() {
  return new PancakeHouseMenuIterator(menuItems);
 }
}
class DinerMenu implements Menu{
 static final int MAX_ITEMS = 6;
 int numberOfItems = 0;
 MenuItem[] menuItems= new MenuItem[MAX_ITEMS];
 public DinerMenu() {  
  addItem("Vegetarian BLT",
    "(Fakin') Bacon with lettuce & tomato on whole wheat", true,
    2.99);
  addItem("BLT", " Bacon with lettuce & tomato on whole wheat", true,
    2.99);
  addItem("Soup of the day",
    "Soup of the day,with a side of potato salad", true, 2.99);
  addItem("Hotdog",
    "A hot dog, with saurkraut,relish,onions,topped with cheese",
    true, 2.99);
 }
 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 not add item to menu!");
  } else {
   menuItems[numberOfItems] = menuItem;
   numberOfItems = numberOfItems + 1;
  }
 }
 public Iterator creatIterator() {
  return new DinerMenuIterator(menuItems);
 }
}
class CafeMenu implements Menu{
 Hashtable menuItems=new Hashtable();
 int position=0;
 public CafeMenu(){
  addItem("Vegegie Burger and Air Fries",
    "Veggie burger on a whole wheat bun,lettuce,tomato,and fries", true,
    3.99);
  addItem("Soup of the day", "A cup of the soup of the day,with a side salad", true,
    2.99);
  addItem("Burrito",
    "A large burrito , with whole pinto beans,salsa,guacamole", true, 2.99);
  
 }
 public void addItem(String name, String description, boolean vegetarian,
   double price) {
  MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
  menuItems.put(position, menuItem);
  position++;
 }
 public Iterator creatIterator() {
  return new CafeMenuIterator(menuItems);
 }
}
interface Iterator {
 boolean hasNext();
 Object next();
 void remove(int i);
}
class DinerMenuIterator implements Iterator {
 MenuItem[] items;
 int position = 0;
 public DinerMenuIterator(MenuItem[] items) {
  this.items = items;
 }
 public boolean hasNext() {
  if (position >= items.length || items[position] == null) {
   return false;
  } else
   return true;
 }
 public Object next() {
  MenuItem menuItem = items[position];
  position = position + 1;
  return menuItem;
 }
 public void remove(int i){
  if(i>=items.length || items[i] == null){
   System.err.println("err");
  }else{
   for(int n=i;n items;
 int position = 0;
 public PancakeHouseMenuIterator(ArrayList items) {
  this.items = items;
 }
 public boolean hasNext() {
  if (position >= items.size()) {
   return false;
  } else
   return true;
 }
 public Object next() {
  MenuItem menuItem = (MenuItem) items.get(position);
  position = position + 1;
  return menuItem;
 }
 @Override
 public void remove(int i) {
  items.remove(i);
 } 
}
 class CafeMenuIterator implements Iterator {
  Hashtable items;  
  int position = 0;
  public CafeMenuIterator(Hashtable items) {
   this.items = items;
  }
  public boolean hasNext() {
   if (position >= items.size()) {
    return false;
   } else
    return true;
  }
  public Object next() {
   MenuItem menuItem = (MenuItem) items.get(position);
   position++;
   return menuItem;
  }
  @Override
  public void remove(int i) {
   items.remove(i);
  } 
 }
 
class AlternatingDinerMenuIterator implements Iterator{
 MenuItem[] items;
 int position;
 public  AlternatingDinerMenuIterator(MenuItem[] items){
  this.items=items;
  Calendar rightNow=Calendar.getInstance();
  position =rightNow.get(Calendar.DAY_OF_WEEK)%2;
 }
 public boolean hasNext(){
  if(position>=items.length||items[position]==null){
   return false;
  }else{
   return true;
  }
 }
 public Object next(){
  MenuItem menuItem=items[position];
  position=position+2;
  return menuItem;
 }
 public void remove(int i){
  throw new UnsupportedOperationException("Alternating Diner Menu Iterator does not support remove()");
 }
}
class Waitress {
 Menu pancakeHouseMenu;
 Menu dinerMenu;
 CafeMenu cafeMenu;
 public Waitress(Menu pancakeHouseMenu, Menu dinerMenu,CafeMenu cafeMenu) {
  this.pancakeHouseMenu = pancakeHouseMenu;
  this.dinerMenu = dinerMenu;
  this.cafeMenu= cafeMenu;
 }
 public void printMenu() {
  Iterator PancakeHouseMenuIterator = pancakeHouseMenu
    .creatIterator();
  Iterator dinerMenuIterator = dinerMenu.creatIterator();
  Iterator  cafeMenuIterator=cafeMenu.creatIterator();
  System.out.println("MENU\n------\nBREAKFAST");
  printMenu(PancakeHouseMenuIterator);
  System.out.println("\nLUNCH");
  printMenu(dinerMenuIterator);
  System.out.println("\nDINNER");
  printMenu(cafeMenuIterator);
 }
 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());
  }
 }
}