迭代器模式提供一种方法顺序访问一个聚合对象中的各个元素，而又不暴露其内部的表示。
示例—合并两种菜单
有两种餐厅菜单，分别用数组和ArrayList实现。现在需要合并两种菜单，且合并后可以让一个女招待的类去访问，不需要重复代码就可以同时访问两种菜单。
UML图表示
迭代器模式-合并菜单
代码演示
菜单项类
package Menu;
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;
}
@Override
public String toString() {
return name + ", " + price + " -- " + description;
}
public String getName() {
return name;
}
public String getDescription() {
return description;
}
public boolean isVegetarian() {
return vegetarian;
}
public double getPrice() {
return price;
}
}
菜单接口
package Menu;
import java.util.Iterator;
public interface Menu {
Iterator createIterator();
}
午餐厅菜单
package Menu;
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);
}
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);
}
}
午餐厅迭代器
package Menu;
import java.util.Iterator;
import java.util.List;
public class DinerMenuIterator implements Iterator {
MenuItem[] items;
int position = 0;
public DinerMenuIterator(MenuItem[] items) {
this.items = items;
}
@Override
public boolean hasNext() {
if (position >= items.length || items[position] == null)
return false;
else
return true;
}
@Override
public Object next() {
MenuItem menuItem = items[position];
position = position + 1;
return menuItem;
}
@Override
public void remove() {
if (position <= 0){
throw new IllegalStateException("You can't remove an item until you've 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;
}
}
}
煎饼屋菜单类
package Menu;
import java.util.ArrayList;
import java.util.Iterator;
public class PancakeHouseMenu implements Menu {
ArrayList煎饼屋迭代器（可用系统迭代器代替）
package Menu;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class PancakeHouseMenuIterator implements Iterator {
private ArrayList服务生类
package Menu;
import java.util.Iterator;
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);
}
public 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());
}
}
}
测试代码
package Menu;
public class MenuTestDrive {
public static void main(String[] args) {
PancakeHouseMenu pancakeHouseMenu = new PancakeHouseMenu();
DinerMenu dinnerMenu = new DinerMenu();
Waitress waitress = new Waitress(pancakeHouseMenu,dinnerMenu);
waitress.printMenu();
}
}
测试结果
MENU
----
BREAKFAST
K&B's Pancake Breakfast, 2.99 -- Pancakes with scrambled eggs, and toast
Regular Pancake Breakfast, 2.99 -- Pancakes with fired 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 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