Head-First-Design-Patterns-master\src\headfirst\designpatterns\iterator

Head-First-Design-Patterns-master\src\headfirst\designpatterns\composite

迭代器模式定義：提供一種方法順序訪問一個集合物件中的各個元素，而又不暴漏其內部的表示

案例：

物件村餐廳和物件村煎餅屋合併了

物件村餐廳選單用的是ArrayList儲存清單

物件村煎餅屋選單用的是資料儲存清單

實現一個java版的服務員。

例如實現取出清單，兩種方法

ArrayList menu 使用menu.get(i)

MenuItem[] menu 使用 menu[i] 

使用迭代器方式相容

ArrayList和陣列都使用   

Iterator it=menu.createIterator();

hasNext（）和next（）方法

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<MenuItem> createIterator() {
        return new DinerMenuIterator(menuItems);
        //return new AlternatingDinerMenuIterator(menuItems);
    }
    // other menu methods here
}

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;
        }
    }
}
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;
    }
}

public interface Menu {
    public Iterator<?> createIterator();
}
 

單一責任：

一個類應該只有一個引起變化的原因

當一個模組或一個類被設計成只支援一組相關的功能時，我們說它具有高內聚。

內聚是比單一責任原則更普遍的概念。

Hashtable也支援迭代器，只不過是對雜湊值的集合的迭代器。

Collection和Iterator的好處在於，每個Collection都知道如何建立自己的Iterator。只要呼叫ArrayList上的Iterator90就可以返回一個具體的Iterator，而你根本不需要知道或者關心到底使用了哪個具體類，你只要使用它的Iterator介面就可以了。

java 5對所有集合的迭代器

for(Object obj: collection){}

當遇到擴充套件子選單的時候，程式碼需要重構了

能夠用樹形來表示選單

定義組合模式：

允許你將物件組合成樹形結構來表示“整體/部分”層次結構，組合能夠讓客戶以一致的方式處理個別對象以及物件組合。

元件、組合、樹的關係：

組合包含元件。元件有兩種：組合與葉節點元素。聽起來像遞迴，組合持有一群孩子，這些孩子可以是別的組合或者葉節點元素。使用這種方式組織資料時，最終會得到樹形結構

使用組合設計選單

建立元件介面
public abstract class MenuComponent {
   
    public void add(MenuComponent menuComponent) {
        throw new UnsupportedOperationException();
    }
    public void remove(MenuComponent menuComponent) {
        throw new UnsupportedOperationException();
    }
    public MenuComponent getChild(int i) {
        throw new UnsupportedOperationException();
    }
  
    public String getName() {
        throw new UnsupportedOperationException();
    }
    public String getDescription() {
        throw new UnsupportedOperationException();
    }
    public double getPrice() {
        throw new UnsupportedOperationException();
    }
    public boolean isVegetarian() {
        throw new UnsupportedOperationException();
    }
  
    public void print() {
        throw new UnsupportedOperationException();
    }
}
//屬於葉節點，具體實現一個菜品
public class MenuItem extends MenuComponent {
    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 void print() {
        System.out.print("  " + getName());
        if (isVegetarian()) {
            System.out.print("(v)");
        }
        System.out.println(", " + getPrice());
        System.out.println("     -- " + getDescription());
    }
}
//選單繼承選單元件是因為，子選單也是在選單中的一個擴充套件，相對葉節點（菜品）來說，選單具有對子選單的一些行為而不是具體實現一個菜品。
public class Menu extends MenuComponent {
    ArrayList<MenuComponent> menuComponents = new ArrayList<MenuComponent>();
    String name;
    String description;
  
    public Menu(String name, String description) {
        this.name = name;
        this.description = description;
    }
    public void add(MenuComponent menuComponent) {
        menuComponents.add(menuComponent);
    }
    public void remove(MenuComponent menuComponent) {
        menuComponents.remove(menuComponent);
    }
    public MenuComponent getChild(int i) {
        return (MenuComponent)menuComponents.get(i);
    }
    public String getName() {
        return name;
    }
    public String getDescription() {
        return description;
    }
    public void print() {
        System.out.print("\n" + getName());
        System.out.println(", " + getDescription());
        System.out.println("---------------------");
  
        Iterator<MenuComponent> iterator = menuComponents.iterator();
        while (iterator.hasNext()) {
            MenuComponent menuComponent =
                (MenuComponent)iterator.next();
            menuComponent.print();
        }
    }
}