(文章翻译自Java Design Pattern: Flyweight)

享元模式用于最小化内存开销。它做的就是使用其他相似的对象尽可能多的分享数据。

1.享元模式类图

2.享元模式Java代码

// Flyweight object interface
interface ICoffee {public void serveCoffee(CoffeeContext context);
}

// Concrete Flyweight object
class Coffee implements ICoffee {private final String flavor;public Coffee(String newFlavor) {this.flavor = newFlavor;System.out.println("Coffee is created! - " + flavor);}public String getFlavor() {return this.flavor;}public void serveCoffee(CoffeeContext context) {System.out.println("Serving " + flavor + " to table " + context.getTable());}
}

// A context, here is table number
class CoffeeContext {private final int tableNumber;public CoffeeContext(int tableNumber) {this.tableNumber = tableNumber;}public int getTable() {return this.tableNumber;}
}

CoffeeFactory：它只是在需要的时候才会创建一个新的咖啡。

//The FlyweightFactory!
class CoffeeFactory {private HashMap<String, Coffee> flavors = new HashMap<String, Coffee>();public Coffee getCoffeeFlavor(String flavorName) {Coffee flavor = flavors.get(flavorName);if (flavor == null) {flavor = new Coffee(flavorName);flavors.put(flavorName, flavor);}return flavor;}public int getTotalCoffeeFlavorsMade() {return flavors.size();}
}

//服务员上咖啡

public class Waitress {//coffee arrayprivate static Coffee[] coffees = new Coffee[20];//table arrayprivate static CoffeeContext[] tables = new CoffeeContext[20];private static int ordersCount = 0;private static CoffeeFactory coffeeFactory;public static void takeOrder(String flavorIn, int table) {coffees[ordersCount] = coffeeFactory.getCoffeeFlavor(flavorIn);tables[ordersCount] = new CoffeeContext(table);ordersCount++;}public static void main(String[] args) {coffeeFactory = new CoffeeFactory();takeOrder("Cappuccino", 2);takeOrder("Cappuccino", 2);takeOrder("Regular Coffee", 1);takeOrder("Regular Coffee", 2);takeOrder("Regular Coffee", 3);takeOrder("Regular Coffee", 4);takeOrder("Cappuccino", 4);takeOrder("Cappuccino", 5);takeOrder("Regular Coffee", 3);takeOrder("Cappuccino", 3);for (int i = 0; i < ordersCount; ++i) {coffees[i].serveCoffee(tables[i]);}System.out.println("\nTotal Coffee objects made: " +  coffeeFactory.getTotalCoffeeFlavorsMade());}
}

检查下面的结果输出，虽然有十个桌子需要咖啡可是只生产了两种咖啡。

Coffee is created! - Cappuccino
Coffee is created! - Regular Coffee
Serving Cappuccino to table 2
Serving Cappuccino to table 2
Serving Regular Coffee to table 1
Serving Regular Coffee to table 2
Serving Regular Coffee to table 3
Serving Regular Coffee to table 4
Serving Cappuccino to table 4
Serving Cappuccino to table 5
Serving Regular Coffee to table 3
Serving Cappuccino to table 3Total Coffee objects made: 2