一、
1.迭代器模式是对遍历集合元素的抽象
2.The Iterator Pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
3.
二、
1.
package headfirst.designpatterns.iterator.dinermerger;
public interface Iterator {
boolean hasNext();
MenuItem next();
}
2.
package headfirst.designpatterns.iterator.dinermerger;
public class DinerMenuIterator implements Iterator {
MenuItem[] items;
int position = 0;
public DinerMenuIterator(MenuItem[] items) {
this.items = items;
}
public MenuItem next() {
MenuItem menuItem = items[position];
position = position + 1;
return menuItem;
}
public boolean hasNext() {
if (position >= items.length || items[position] == null) {
return false;
} else {
return true;
}
}
}
3.
package headfirst.designpatterns.iterator.dinermerger;
import java.util.ArrayList;
public class PancakeHouseMenuIterator implements Iterator {
ArrayList<MenuItem> items;
int position = 0;
public PancakeHouseMenuIterator(ArrayList<MenuItem> items) {
this.items = items;
}
public MenuItem next() {
MenuItem item = items.get(position);
position = position + 1;
return item;
}
public boolean hasNext() {
if (position >= items.size()) {
return false;
} else {
return true;
}
}
}
4.
package headfirst.designpatterns.iterator.dinermerger;
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, 3.29);
addItem("Hotdog",
"A hot dog, with saurkraut, relish, onions, topped with cheese",
false, 3.05);
addItem("Steamed Veggies and Brown Rice",
"Steamed vegetables over brown rice", true, 3.99);
addItem("Pasta",
"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
true, 3.89);
}
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 = numberOfItems + 1;
}
}
public MenuItem[] getMenuItems() {
return menuItems;
}
public Iterator createIterator() {
return new DinerMenuIterator(menuItems);
// To test Alternating menu items, comment out above line,
// and uncomment the line below.
//return new AlternatingDinerMenuIterator(menuItems);
}
// other menu methods here
}
5.
package headfirst.designpatterns.iterator.dinermerger;
import java.util.ArrayList;
public class PancakeHouseMenu implements Menu {
ArrayList<MenuItem> menuItems;
public PancakeHouseMenu() {
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 ArrayList<MenuItem> getMenuItems() {
return menuItems;
}
public Iterator createIterator() {
return new PancakeHouseMenuIterator(menuItems);
}
public String toString() {
return "Objectville Pancake House Menu";
}
// other menu methods here
}
6.
package headfirst.designpatterns.iterator.dinermerger;
public interface Menu {
public Iterator createIterator();
}
7.
package headfirst.designpatterns.iterator.dinermerger;
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 description;
}
public double getPrice() {
return price;
}
public boolean isVegetarian() {
return vegetarian;
}
public String toString() {
return (name + ", $" + price + "\n " + description);
}
}
8.
package headfirst.designpatterns.iterator.dinermerger;
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 = iterator.next();
System.out.print(menuItem.getName() + ", ");
System.out.print(menuItem.getPrice() + " -- ");
System.out.println(menuItem.getDescription());
}
}
public void printVegetarianMenu() {
printVegetarianMenu(pancakeHouseMenu.createIterator());
printVegetarianMenu(dinerMenu.createIterator());
}
public boolean isItemVegetarian(String name) {
Iterator breakfastIterator = pancakeHouseMenu.createIterator();
if (isVegetarian(name, breakfastIterator)) {
return true;
}
Iterator dinnerIterator = dinerMenu.createIterator();
if (isVegetarian(name, dinnerIterator)) {
return true;
}
return false;
}
private void printVegetarianMenu(Iterator iterator) {
while (iterator.hasNext()) {
MenuItem menuItem = iterator.next();
if (menuItem.isVegetarian()) {
System.out.print(menuItem.getName());
System.out.println("\t\t" + menuItem.getPrice());
System.out.println("\t" + menuItem.getDescription());
}
}
}
private boolean isVegetarian(String name, Iterator iterator) {
while (iterator.hasNext()) {
MenuItem menuItem = iterator.next();
if (menuItem.getName().equals(name)) {
if (menuItem.isVegetarian()) {
return true;
}
}
}
return false;
}
}
9.
package headfirst.designpatterns.iterator.dinermerger;
import java.util.*;
public class MenuTestDrive {
public static void main(String args[]) {
PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
DinerMenu dinerMenu = new DinerMenu();
Waitress waitress = new Waitress(pancakeHouseMenu, dinerMenu);
// Without iterators
//printMenu();
// With iterators
waitress.printMenu();
}
/*
* Without the Waitress, we need the code below...
*/
public static void printMenu() {
PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
DinerMenu dinerMenu = new DinerMenu();
ArrayList<MenuItem> breakfastItems = pancakeHouseMenu.getMenuItems();
MenuItem[] lunchItems = dinerMenu.getMenuItems();
// Hiding implementation
System.out.println("USING FOR EACH");
for (MenuItem menuItem : breakfastItems) {
System.out.print(menuItem.getName());
System.out.println("\t\t" + menuItem.getPrice());
System.out.println("\t" + menuItem.getDescription());
}
for (MenuItem menuItem : lunchItems) {
System.out.print(menuItem.getName());
System.out.println("\t\t" + menuItem.getPrice());
System.out.println("\t" + menuItem.getDescription());
}
// Exposing implementation
System.out.println("USING FOR LOOPS");
for (int i = 0; i < breakfastItems.size(); i++) {
MenuItem menuItem = (MenuItem)breakfastItems.get(i);
System.out.print(menuItem.getName());
System.out.println("\t\t" + menuItem.getPrice());
System.out.println("\t" + menuItem.getDescription());
}
for (int i = 0; i < lunchItems.length; i++) {
MenuItem menuItem = lunchItems[i];
System.out.print(menuItem.getName());
System.out.println("\t\t" + menuItem.getPrice());
System.out.println("\t" + menuItem.getDescription());
}
}
}
三、用java.util.Iterator
1.
package headfirst.designpatterns.iterator.dinermergercafe;
import java.util.Iterator;
public class DinerMenuIterator implements Iterator<MenuItem> {
MenuItem[] list;
int position = 0;
public DinerMenuIterator(MenuItem[] list) {
this.list = list;
}
public MenuItem next() {
MenuItem menuItem = list[position];
position = position + 1;
return menuItem;
}
public boolean hasNext() {
if (position >= list.length || list[position] == null) {
return false;
} else {
return true;
}
}
public void remove() {
if (position <= 0) {
throw new IllegalStateException
("You can't remove an item until you've done at least one next()");
}
if (list[position-1] != null) {
for (int i = position-1; i < (list.length-1); i++) {
list[i] = list[i+1];
}
list[list.length-1] = null;
}
}
}
2.
package headfirst.designpatterns.iterator.dinermergercafe;
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, 3.29);
addItem("Hotdog",
"A hot dog, with saurkraut, relish, onions, topped with cheese",
false, 3.05);
addItem("Steamed Veggies and Brown Rice",
"A medly of steamed vegetables over brown rice", true, 3.99);
addItem("Pasta",
"Spaghetti with Marinara Sauce, and a slice of sourdough bread",
true, 3.89);
}
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 = numberOfItems + 1;
}
}
public MenuItem[] getMenuItems() {
return menuItems;
}
public Iterator<MenuItem> createIterator() {
return new DinerMenuIterator(menuItems);
//return new AlternatingDinerMenuIterator(menuItems);
}
// other menu methods here
}
3.用hashmap
package headfirst.designpatterns.iterator.dinermergercafe;
import java.util.*;
public class CafeMenu implements Menu {
HashMap<String, MenuItem> menuItems = new HashMap<String, MenuItem>();
public CafeMenu() {
addItem("Veggie 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",
false, 3.69);
addItem("Burrito",
"A large burrito, with whole pinto beans, salsa, guacamole",
true, 4.29);
}
public void addItem(String name, String description,
boolean vegetarian, double price)
{
MenuItem menuItem = new MenuItem(name, description, vegetarian, price);
menuItems.put(menuItem.getName(), menuItem);
}
public Map<String, MenuItem> getItems() {
return menuItems;
}
public Iterator<MenuItem> createIterator() {
return menuItems.values().iterator();
}
}