Create objects, rather than having to instantiate objects directly. This gives the program more flexibility in deciding which objects need to be created for a given case.
- Groups object factories that have a common theme.
- Constructs complex objects by separating construction and representation.
- Creates objects without specifying the exact class to create.
- Creates objects by cloning an existing object.
- Restricts object creation for a class to only one instance.
Concern class and object composition. They use inheritance to compose interfaces and define ways to compose objects to obtain new functionality.
- Allows classes with incompatible interfaces to work together by wrapping its own interface around that of an already existing class.
- Decouples an abstraction from its implementation so that the two can vary independently.
- Composes zero-or-more similar objects so that they can be manipulated as one object.
- Dynamically adds/overrides behavior in an existing method of an object.
- Provides a simplified interface to a large body of code.
- Reduces the cost of creating and manipulating a large number of similar objects.
- Provides a placeholder for another object to control access, reduce cost, and reduce complexity.
Specifically concerned with communication between objects.
- Delegates commands to a chain of processing objects.
- Creates objects that encapsulate actions and parameters.
- Implements a specialized language.
- Accesses the elements of an object sequentially without exposing its underlying representation.
- Allows loose coupling between classes by being the only class that has detailed knowledge of their methods.
- Provides the ability to restore an object to its previous state (undo).
- Is a publish/subscribe pattern, which allows a number of observer objects to see an event.
- Allows an object to alter its behavior when its internal state changes.
- Allows one of a family of algorithms to be selected on-the-fly at runtime.
- Defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior.
- Separates an algorithm from an object structure by moving the hierarchy of methods into one object.