Decorator Pattern - sivakrsna/DesignPatterns GitHub Wiki

The Decorator Pattern attaches additional responsibilities to an object dynamically. Decorators provide a fl exible alternative to subclassing for extending functionality.

Key Points

• Decorators have the same supertype as the objects they decorate.
• You can use one or more decorators to wrap an object.
• Given that the decorator has the same supertype as the object it decorates, we can pass around a decorated object in place of the original (wrapped) object.
• The decorator adds its own behavior either before and/or after delegating to the object it decorates to do the rest of the job.
• Objects can be decorated at any time, so we can decorate objects dynamically at runtime with as many decorators as we like.

Real time Example

Example

public class StarbuzzCoffee {
 public static void main(String args[]) {
   Beverage beverage = new Espresso();
   System.out.println(beverage.getDescription()
      + “ $” + beverage.cost());
   Beverage beverage2 = new DarkRoast();
   beverage2 = new Mocha(beverage2);
   beverage2 = new Mocha(beverage2);
   beverage2 = new Whip(beverage2);
   System.out.println(beverage2.getDescription()
         + “ $” + beverage2.cost());
   Beverage beverage3 = new HouseBlend();
   beverage3 = new Soy(beverage3);
   beverage3 = new Mocha(beverage3);
   beverage3 = new Whip(beverage3);
   System.out.println(beverage3.getDescription()
    + “ $” + beverage3.cost());
 }
}

public abstract class Beverage {
   String description = “Unknown Beverage”;
   public String getDescription() {
     return description;
   }
   public abstract double cost();
   }
}

public abstract class CondimentDecorator extends Beverage {
   public abstract String getDescription();
}

public class Espresso extends Beverage {
   public Espresso() {
     description = “Espresso”;
   }
   public double cost() {
     return 1.99;
   }
}