// The abstract Coffee class defines the functionality of Coffee implemented by decorator
public abstract class Coffee {public abstract double getCost(); // Returns the cost of the coffeepublic abstract String getIngredients(); // Returns the ingredients of the coffee
}// Extension of a simple coffee without any extra ingredients
public class SimpleCoffee extends Coffee {public double getCost() {return 1;}public String getIngredients() {return "Coffee";}
}

// Abstract decorator class - note that it extends Coffee abstract class
public abstract class CoffeeDecorator extends Coffee {protected final Coffee decoratedCoffee;protected String ingredientSeparator = ", ";public CoffeeDecorator (Coffee decoratedCoffee) {this.decoratedCoffee = decoratedCoffee;}public double getCost() { // Implementing methods of the abstract classreturn decoratedCoffee.getCost();}public String getIngredients() {return decoratedCoffee.getIngredients();}
}

// Decorator Milk that mixes milk with coffee.
// Note it extends CoffeeDecorator.
class Milk extends CoffeeDecorator {public Milk (Coffee decoratedCoffee) {super(decoratedCoffee);}public double getCost() { // Overriding methods defined in the abstract superclassreturn super.getCost() + 0.5;}public String getIngredients() {return super.getIngredients() + ingredientSeparator + "Milk";}
}// Decorator Whip that mixes whip with coffee.
// Note it extends CoffeeDecorator.
class Whip extends CoffeeDecorator {public Whip (Coffee decoratedCoffee) {super(decoratedCoffee);}public double getCost() {return super.getCost() + 0.7;}public String getIngredients() {return super.getIngredients() + ingredientSeparator + "Whip";}
}// Decorator Sprinkles that mixes sprinkles with coffee.
// Note it extends CoffeeDecorator.
class Sprinkles extends CoffeeDecorator {public Sprinkles (Coffee decoratedCoffee) {super(decoratedCoffee);}public double getCost() {return super.getCost() + 0.2;}public String getIngredients() {return super.getIngredients() + ingredientSeparator + "Sprinkles";}
}

public class Main {public static final void main(String[] args) {Coffee c = new SimpleCoffee();System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());c = new Milk(c);System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());c = new Sprinkles(c);System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());c = new Whip(c);System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());// Note that you can also stack more than one decorator of the same typec = new Sprinkles(c);System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());}}

Cost: 1.0; Ingredients: Coffee
Cost: 1.5; Ingredients: Coffee, Milk
Cost: 1.7; Ingredients: Coffee, Milk, Sprinkles
Cost: 2.4; Ingredients: Coffee, Milk, Sprinkles, Whip
Cost: 2.6; Ingredients: Coffee, Milk, Sprinkles, Whip, Sprinkles

Decorator模式有以下的优缺点：

1.      比静态继承更灵活 与对象的静态继承相比，Decorator模式提供了更加灵活的向对象添加职责的方式，可以使用添加和分离的方法，用装饰在运行时刻增加和删除职责。使用继承机制增加职责需要创建一个新的子            类，如果需要为原来所有的子类都添加功能的话，每个子类都需要重写，增加系统的复杂度，此外可以为一个特定的Component类提供多个Decorator，这种混合匹配是适用继承很难做到的。

2.      避免在层次结构高层的类有太多的特征，Decorator模式提供了一种“即用即付”的方法来添加职责，他并不试图在一个复杂的可订制的类中支持所有可预见的特征，相反可以定义一个简单的类，并且用Decorator            类给他逐渐的添加功能，可以从简单的部件组合出复杂的功能。

3.      Decorator 与它的Component不一样 Decorator是一个透明的包装，如果我们从对象标识的观点出发，一个被装饰了的组件与这个组件是有差别的，因此使用装饰时不应该以来对象标识。

4.      产生许多小对象，采用Decorator模式进行系统设计往往会产生许多看上去类似的小对象，这些对象仅仅在他们相互连接的方式上有所不同。