(Single Factory Builds Prototypes)
Singleton Pattern (Creational) :
Ensure a class has only one instance, and provide a global point of access to it.
Encapsulated “just-in-time initialization” or “initialization on first use”.
Example: The office of the President of the United States is a Singleton.
Example: Logger Class, Configuration Class
Reference: http://www.oodesign.com/singleton-pattern.html
Factory Pattern (Creational) :
– (Similar to Abstract Factory Pattern)
– One of the most used patterns in programming
– Define an interface for creating an object, but let subclasses decide which class to instantiate (usually with the help of a type parameter). Factory Method lets a class defer instantiation to subclasses.Defining a “virtual” constructor.
– creates objects without exposing the instantiation logic to the client. and refers to the newly created object through a common interface
Example:
For example a graphical application works with shapes. In our implementation the drawing framework is the client and the shapes are the products. All the shapes are derived from an abstract shape class (or interface). The Shape class defines the draw and move operations which must be implemented by the concrete shapes. Let’s assume a command is selected from the menu to create a new Circle. The framework receives the shape type as a string parameter, it asks the factory to create a new shape sending the parameter received from menu. The factory creates a new circle and returns it to the framework, casted to an abstract shape. Then the framework uses the object as casted to the abstract class without being aware of the concrete object type.
Example: Injection molding presses demonstrate this pattern. Manufacturers of plastic toys process plastic molding powder, and inject the plastic into molds of the desired shapes. The class of toy (car, action figure, etc.) is determined by the mold.
http://www.oodesign.com/factory-pattern.html
Builder Design Pattern (Creational) :
Builder is a creational design pattern that lets you construct complex objects step by step. The pattern allows you to produce different types and representations of an object using the same construction code. Separate the construction of a complex object from its representation so that the same construction process can create different representations.Parse a complex representation, create one of several targets. It is a mechanism for building complex objects that is independent from the ones that make up the object.
The “director” invokes “builder” services as it interprets the external format. The “builder” creates part of the complex object each time it is called and maintains all intermediate state. When the product is finished, the client retrieves the result from the “builder”.
Example: This pattern is used by fast food restaurants to construct children’s meals. Children’s meals typically consist of a main item, a side item, a drink, and a toy (e.g., a hamburger, fries, Coke, and toy dinosaur). Note that there can be variation in the content of the children’s meal, but the construction process is the same. Whether a customer orders a hamburger, cheeseburger, or chicken, the process is the same. The employee at the counter directs the crew to assemble a main item, side item, and toy.
http://www.oodesign.com/builder-pattern.html
The Builder design pattern is very similar, at some extent, to the Abstract Factory pattern. That?s why it is important to be able to make the difference between the situations when one or the other is used. In the case of the Abstract Factory, the client uses the factory?s methods to create its own objects. In the Builder?s case, the Builder class is instructed on how to create the object and then it is asked for it, but the way that the class is put together is up to the Builder class, this detail making the difference between the two patterns.
Prototype Pattern:
Prototype pattern refers to creating duplicate object while keeping performance in mind. This pattern involves implementing a prototype interface which tells to create a clone of the current object. This pattern is used when creation of object directly is costly. For example, a object is to be created after a costly database operation. We can cache the object, returns its clone on next request and update the database as as and when needed thus reducing database calls.