結構型設計模式-享元模式

什麼是享元模式

享元模式爲運用共享技術有效的支持大量細粒度的對象。因爲它可以通過共享大幅度地減少單個實例的數目，避免了大量非常相似類的開銷。
享元模式是一個類別的多個對象共享這個類別的一個對象，而不是各自再實例化各自的對象。這樣就達到了節省內存的目的。

實現享元模式

// Instances of CoffeeFlavour will be the Flyweights
class CoffeeFlavour {
  private final String name;

  CoffeeFlavour(String newFlavor) {
    this.name = newFlavor;
  }

  @Override
  public String toString() {
    return name;
  }
}

// Menu acts as a factory and cache for CoffeeFlavour flyweight objects
class Menu {
  private Map<String, CoffeeFlavour> flavours = new ConcurrentHashMap<String, CoffeeFlavour>();

  CoffeeFlavour lookup(String flavorName) {
    if (!flavours.containsKey(flavorName))
      flavours.put(flavorName, new CoffeeFlavour(flavorName));
    return flavours.get(flavorName);
  }

  int totalCoffeeFlavoursMade() {
    return flavours.size();
  }
}

class Order {
  private final int tableNumber;
  private final CoffeeFlavour flavour;

  Order(int tableNumber, CoffeeFlavour flavor) {
    this.tableNumber = tableNumber;
    this.flavour = flavor;
  }

  void serve() {
    System.out.println("Serving " + flavour + " to table " + tableNumber);
  }
}

public class CoffeeShop {
  private final List<Order> orders = new Vector<Order>();
  private final Menu menu = new Menu();

  void takeOrder(String flavourName, int table) {
    CoffeeFlavour flavour = menu.lookup(flavourName);
    Order order = new Order(table, flavour);
    orders.add(order);
  }

  void service() {
    for (Order order : orders)
      order.serve();
  }

  String report() {
    return "\ntotal CoffeeFlavour objects made: "
        + menu.totalCoffeeFlavoursMade();
  }

  public static void main(String[] args) {
    CoffeeShop shop = new CoffeeShop();

    shop.takeOrder("Cappuccino", 2);
    shop.takeOrder("Frappe", 1);
    shop.takeOrder("Espresso", 1);
    shop.takeOrder("Frappe", 897);
    shop.takeOrder("Cappuccino", 97);
    shop.takeOrder("Frappe", 3);
    shop.takeOrder("Espresso", 3);
    shop.takeOrder("Cappuccino", 3);
    shop.takeOrder("Espresso", 96);
    shop.takeOrder("Frappe", 552);
    shop.takeOrder("Cappuccino", 121);
    shop.takeOrder("Espresso", 121);

    shop.service();
    System.out.println(shop.report());
  }
}