Convert the interface of a class into another interface clients expect. It lets classes work together that couldn't otherwise because of incompatible interfaces.

Decouple an abstraction from its implementation so that the two can vary independently.

Compose objects into tree structures to represent part-whole hierarchies. It lets clients treat individual objects and compositions of objects uniformly.

Attach additional responsibilities to an object dynamically. Provides a flexible alternative to subclassing for extending functionality.

Provide a unified interface to a set of interfaces in a subsystem. Defines a higher-level interface that makes the subsystem easier to use.

Use sharing to support large numbers of fine-grained objects efficiently

Provide a surrogate or placeholder for another object to control access to it.

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.

Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.

Avoid expensive acquisition and release of resources by recycling objects that are no longer in use

Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.

Ensure a class only has one instance, and provide a global point of access to it.

A class with a private constructor that contains only static methods.

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 undoable operations.

Given a language, define a representation for its grammar and uses the representation to interpret sentences in the language.

Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Define an object that encapsulates how a set of objects interact. Promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.

Define a one-to-many dependency between objects 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. It lets the algorithm vary independently from clients that use it.

Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. It lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

Represent an operation to be performed on the elements of an object structure. It lets you define a new operation without changing the classes of the elements on which it operates.