12) Flyweight Pattern

类别：

 Structural Pattern

问题/动机：

假若绿色是相同部分，占用1M内存 ，如果提取出来，众对象共享其内容，只占1M内存 ，否则占10M ，且随着对象增多，占用越来越多内存 ，无疑是浪费资源

A flyweight is an object that minimizes memory usage by sharing as much data as possible with other similar objects （通过共享来削减内存）

方案：

示例：

import java.util.List;
import java.util.Map;
import java.util.Vector;
import java.util.concurrent.ConcurrentHashMap;

public class FlyweightPatternDemo {

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

        shop.takeOrder("Cappuccino", 2);
        shop.takeOrder("Latte", 1);
        shop.takeOrder("Macchiato", 1);
        shop.takeOrder("Latte", 4);
        shop.takeOrder("Cappuccino", 5);
        shop.takeOrder("Latte", 3);
        shop.takeOrder("Macchiato", 3);
        shop.takeOrder("Cappuccino", 3);
        shop.takeOrder("Macchiato", 5);
        shop.takeOrder("Latte", 5);
        shop.takeOrder("Cappuccino", 3);
        shop.takeOrder("Macchiato", 5);

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

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

    Coffee(final String name) {
        this.name = name;
    }

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

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

    synchronized Coffee lookup(final String name) {
        if (!coffeeMap.containsKey(name))
            coffeeMap.put(name, new Coffee(name));
        return coffeeMap.get(name);
    }

    synchronized int totalCoffeeMade() {
        return coffeeMap.size();
    }
}

// Order is the context of the CoffeeFlavour flyweight.
class Order {
    private final int tableNumber;
    private final Coffee coffee;

    Order(final int tableNumber, final Coffee coffee) {
        this.tableNumber = tableNumber;
        this.coffee = coffee;
    }

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

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

    void takeOrder(final String name, final int table) {
        Coffee coffee = menu.lookup(name);
        Order order = new Order(table, coffee);
        orders.add(order);
    }

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

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

}

Serving Cappuccino to table 2
Serving Latte to table 1
Serving Macchiato to table 1
Serving Latte to table 4
Serving Cappuccino to table 5
Serving Latte to table 3
Serving Macchiato to table 3
Serving Cappuccino to table 3
Serving Macchiato to table 5
Serving Latte to table 5
Serving Cappuccino to table 3
Serving Macchiato to table 5

total coffee objects made: 3

应用：

不足：(

优化：）