[译]ava 设计模式之享元

(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 array
   private static Coffee[] coffees = new Coffee[20];
   //table array
   private 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("
Total 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 3

Total Coffee objects made: 2