The Open-Closed Principle

Meet the Decorator Pattern

• 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 before and/or after delegating to the object it decorates to do the rest of the job.

  The Decorator Pattern defined

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

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

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

  ```java public class Espresso extends Beverage {

  public Espresso() {

    description = "Espresso";

  }

  public double cost() {

    return 1.99;

  } }

public class HouseBlend extends Beverage { public HouseBlend() { description = “House Blend Coffee”; }

public double cost() {
    return .89;
}

}

```java
public class Mocha extends CondimentDecorator {
    public Mocha(Beverage beverage) {
        this.beverage = beverage;
    }
    public String getDescription() {
        return beverage.getDescription() + ", Mocha";
    }
    public double cost() {
        return .20 + beverage.cost();
    }
}
public class Soy extends CondimentDecorator {
    public Soy(Beverage beverage) {
        this.beverage = beverage;
    }
    public String getDescription() {
        return beverage.getDescription() + ", Soy";
    }
    public double cost() {
        return .15 + beverage.cost();
    }
}