Head First Design Patterns - Decorator Pattern
Design Principle(Open-Closed Principle)
- Classes should be open for extension, but closed for modification.
The Decorator Pattern attaches additional responsibilitis to an object dynamically.
Decorator 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{
public abstract String getDescription();
}
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 0.89;
}
}
public class Mocha extends CondimentDecorator{
Beverage beverage;
public Mocha(Beverage beverage){
this.beverage = beverage;
}
public String getDescription(){
return beverage.getDescription +", Mocha";
}
public double cost(){
return 0.20 + beverage.cost();
}
}
