Intent: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Applicability: Use the Abstract Factory pattern when
- a system should be independent of how its products are created, composed and represented
- a system should be configured with one of multiple families of products
- a family of related product objects is designed to be used together, and you need to enforce this constraint
- you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
Intent: Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Applicability: Use the Builder pattern when
- the algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled
- the construction process must allow different representations for the object that's constructed
Intent: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
Applicability: Use the Factory Method pattern when
- a class can't anticipate the class of objects it must create
- a class wants its subclasses to specify the objects it creates
- classes delegate responsibility to one of several helper subclasses, and you want to localize the knowledge of which helper subclass is the delegate
Intent: Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
Applicability: Use the Prototype pattern when a system should be independent of how its products are created, composed and represented; and
- when the classes to instantiate are specified at run-time, for example, by dynamic loading; or
- to avoid building a class hierarchy of factories that parallels the class hierarchy of products; or
- when instances of a class can have one of only a few different combinations of state. It may be more convenient to install a corresponding number of prototypes and clone them rather than instantiating the class manually, each time with the appropriate state