Design Patterns
Creational Patterns
Factory Method
Define an interface for creating an object, but let subclasses decide which class to instantiate. Returns one of several different subclasses, depending on the data passed in arguments to the creation methods.
Abstract Factory
Define an interface for creating families of related or dependent objects without specifying their concrete classes.
Singleton
Singleton pattern is a class of which there may be no more than one instance. It provides a single global point of access to that instance. For ex. Print Spooler.
Builder
Separate the construction of a complex object from its representation so that the same construction process can create different representations.
Prototype
Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype. For ex. Java Cloning.
Structural Patterns
Adapter
Convert the interface of a class into another interface clients expect.
Decouple an abstraction from its implementation so that the two can vary independently.
Composite
Compose objects into tree structures to represent part-whole hierarchies. A composite is a collection of objects, any one of which may be either a composite or primitive object.
Decorator
Attach additional responsibilities to an object dynamically. A flexible alternative to subclassing. Modifies the behavior of individual objects without having to create a derived class.
Facade
Provide a unified interface for a set of interfaces in a subsystem. It is a way of hiding a complex system inside a simpler interface.
Flyweight
Use sharing to support large numbers of fine-grained objects efficiently. Each instance does not contain its own state, but stores it externally.
Proxy
Provide a surrogate or placeholder for another object to control access to it.
Behavioral Patterns
Chain of Responsibility
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. Commonly used for parsers and even compilers.
Command
Encapsulate request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
Interpreter
Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
Iterator
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. For ex, Enumeration
Mediator
Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping object from referring to each other explicitly, and it lets you vary their interaction independently.
Memento
Without violating encapsulation, capture and externalize an objects internal state so that the object can be restored to this state later.
Observer
Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
State
Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
Strategy
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
Template Method
Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure. For ex. An Abstract Class
Visitor
Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.