Previously I discussed
Strategy Pattern
Factory Pattern
Abstract Factory Pattern
Observer Pattern
Facade Pattern
Today I'll be discussing the Builder Pattern. I usually don't include UML because they are all over the web and haven't brought that much extra value to my write-ups. But this pattern has a few more parts then the previous patterns I have dicussed, and I feel it will help.
Straight from Wikipedia
The builder pattern is a creational pattern, and the point of it is to encapsulate the complexities of creating a
complicated object. The Builder pattern can also create variations of the complex object.
At first I thought this pattern sounded familiar. It sounded a little bit like the Factory or Factory Method Pattern or maybe Abstract Factory. Its pretty different though and a short definition of each should help illustrate.
Factory - Client calls factory and factory directly returns one of many different types based on the parameters given to it. The clinet doesn't know what it's getting back only that the object inherits from a given abstract class or interface.
Factory Method - Client has an instance of an abscract factory wich defines an abstract method for creating products, but the client instantiates the factory with a conrete instance of that factory. The concrete instance impliments the create method and can create one of many types of the product but only return the parent class or interface that represents the product.
Abstract Factory - There are some similarities to the Factory method pattern here but just remember the Factory method pattern only returns one parent type to the client. In Abstract Facotry the client has a reference to an abstract factory, and instanciates it with a concreate factory that implements the abstract factory. The concrete factory creates concrete products and returns multiple parent types to the client.
Builder Pattern - An abstract builder class defines abstract methods for creating various parts, and a method for returning a product. Concrete builders implement the abstract builder class and are responcible for building the parts, keeping track of their representations and providing a method to return the final product. A director class provides a construction method that calls the part building methods in the concrete builder classes. (In what ever order or with what ever parameters it decides on).
Below is my car demonstration of the Builder pattern. The source code along with all other pattern examples can be found here
