Design Patterns in One Sentence

Factory Method

The abstract class focuses on business logic, while its subclasses determine the implementation details.

Abstract Factory

2D factory method. Create different products of the same variant.

Builder

Create product part by part, usually in chain.

Prototype

Provide a method to clone itself.

Singleton

Always return the same instance.

Adapter

Encapsulate an instance of old class, and provide new interface to the outside.

Bridge

Different abstraction layer and different implementation layer can be mixed at will.

Composition

A tree where all nodes provide the same interface, the leaves do the job, and non-leaves aggregate the results of their own leaves.

Decorator

Encapsulate an instance of a class, and provide the same interface to the outside.

Facade

Encapsulate complicated logic, and provide simple interface to the outside.

Flyweight

Create a new class for those memory-consuming, shared attributes, for which a factory is created for caching.

Proxy

Encapsulate an instance of a class, provide the same interface to the outside, and manage the lifecycle of the internal instance.

Chain of Responsibility

Process an object through a chain, where each link can determine whether to continue or terminate processing.

Command

Abstract a callback function as a class, and makes it fetch arguments - explicitly on initialization or on its own - every time the command is executed.

Iterator

Encapsulate an instance of a class, and provide the iteration method of this instance.

Mediator

Elements in a system send their interaction information to the mediator, and listen to its schedule, rather than directly interacting with each other.

Memento

Create snapshots of another class.

Observer

The object notifies all of its observers of its latest update.

State

Divide a class with volatile states into state and context, where the state executes all state-related operations and can modify the state on its own.

Strategy

Abstract different strategies into classes, and let the business logic pick which one to use.

Template Method

The template parent class implements a set of standard methods, while its subclasses overload methods according to their needs.

Visitor

The visited class redirects request to the visitor, who extends the interface of the visited class.