Ensure a class only has one instance, and provide a global point of access to it.
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Specify the kind of objects to create using the prototypical instance, and create new objects by copying this prototype.
For classes use inheritance.
Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Methods lets a class defer instantiation to subclasses.
Convert the interface of a class into another clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
Provide a surrogate or palceholder for another object to control access to it.
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
Attach additional responsibilities to an object dynamically/ Decorators provide a flexible alternative to subclassing for extending functionality.
Avoid coupling the sender of a request to its receiver by giving more than one object of a change to handle the request. Chain the receiving objects and pass the request along the chain.
Encapsulate a request as an object, thereby letting you parameterize with different request. queue or log requests, and support undoable operations.
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representations.
Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.