Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
List the collaborations involved with using "Builder"
- 1. Client creates a "Director" and a "Concrete Builder" instance (a "Builder" subclass for a particular representation), passing the latter to the former. - 2. Client tells the Director to construct the object. - 3. Director directs Builder to build an object (the "Product") by calling its methods. - 4. Client gets Product from Builder subclass instance.
Define an interface for creating an object, but let subclasses decide which class to instantiate. Lets a class defer instantiation to subclasses.
Specify the kinds of objects to create using a prototypical instance and create new objects by copying this prototype.
Ensure a class has only one instance and provide a global point of access to it.
Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.
Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undo operations.
Given a language, define a representation for its grammar, along with a system that uses the representation to interpret sentences in the language.
Provide a way to access the elements of an aggregate object sequentially with out exposing its underlying implementation.
Define an object that encapsulates how a set of objects interact. Promotes loose coupling by keeping objects from referring to each other explicitly, and lets you vary their interaction independently.
Without violating encapsulation, capture and externalize an object's internal state so that objects can be restored to this state later.
Define a one-to-many dependency so that when one object changes state, all its dependents are notified and updated automatically.
Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
Define a family of algorithms, encapsulate each one, and make them interchangeable. Lets the algorithm vary independently from the clients that use it.
Define the skeleton of an algorithm in an operation, deferring some steps to its subclasses. Lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
Represent an operation to be performed on elements of an object structure. Lets you define a new operation without changing the classes of the elements on which it operates.