The document summarizes 23 design patterns organized into three categories: Creational patterns, Structural patterns, and Behavioral patterns. Each pattern lists the pattern name, intent, participants, and collaborations in 1-2 sentences. For example, the Singleton pattern ensures a class only has one instance and provides a global point of access to it.

1. C Abstract Factory S Facade S Proxy Memento
Memento
-state
Caretaker
B Observer
S Adapter C Factory Method
Type: Behavioral
C Singleton
S Bridge S Flyweight
What it is:
Without violating encapsulation, capture
B State
C Builder B Interpreter
and externalize an object's internal state
so that the object can be restored to this
B Strategy
B Chain of Responsibility B Iterator Originator
state later.
-state
B Template Method
B Command B Mediator
+setMemento(in m : Memento)
B Visitor
S Composite B Memento +createMemento()
S Decorator C Prototype
«interface»
notifies
Observer
Chain of Responsibility «interface»
successor
«interface» Subject
Observer
Handler +attach(in o : Observer)
Client
Type: Behavioral +update()
Type: Behavioral
+handleRequest() +detach(in o : Observer)
+notify()
What it is:
What it is:
Define a one-to-many dependency between
Avoid coupling the sender of a request to
objects so that when one object changes
its receiver by giving more than one object
state, all its dependents are notified and
a chance to handle the request. Chain the
updated automatically.
receiving objects and pass the request
ConcreteSubject ConcreteObserver
observes
along the chain until an object handles it.
ConcreteHandler1 ConcreteHandler2
-subjectState -observerState
+handleRequest() +handleRequest()
+update()
Command State Context
Client Invoker
+request()
Type: Behavioral «interface»
Type: Behavioral
State
ConcreteCommand What it is:
What it is: +handle()
Allow an object to alter its behavior when
Encapsulate a request as an object,
+execute()
its internal state changes. The object will
thereby letting you parameterize clients
appear to change its class.
with different requests, queue or log
requests, and support undoable operations.
Command
Receiver
+execute() ConcreteState1 ConcreteState2
+action()
+handle() +handle()
Strategy
Client
Interpreter Context
Type: Behavioral «interface»
Type: Behavioral Strategy
«interface»
What it is:
+execute()
AbstractExpression
Context What it is: Define a family of algorithms,
+interpret() Given a language, define a representation encapsulate each one, and make them
for its grammar along with an interpreter interchangeable. Lets the algorithm vary
that uses the representation to interpret independently from
sentences in the language. clients that use it.
ConcreteStrategyA ConcreteStrategyB
TerminalExpression NonterminalExpression +execute() +execute()
+interpret() : Context +interpret() : Context
Client
Template Method
Iterator AbstractClass
+templateMethod()
Type: Behavioral
Type: Behavioral
«interface»
«interface» #subMethod()
Iterator
Aggregate What it is:
What it is:
+next() Define the skeleton of an algorithm in an
+createIterator() Provide a way to access the elements of
operation, deferring some steps to subclasses.
an aggregate object sequentially without
Lets subclasses redefine certain steps
exposing its underlying representation.
of an algorithm without changing the
ConcreteClass
algorithm's structure.
ConcreteIterator +subMethod()
ConcreteAggregate
+next() : Context
+createIterator() : Context
«interface»
Visitor
informs
Mediator Visitor
«interface» Client
Mediator +visitElementA(in a : ConcreteElementA)
Type: Behavioral
Colleague
Type: Behavioral +visitElementB(in b : ConcreteElementB)
What it is:
What it is: «interface»
Represent an operation to be
Define an object that encapsulates how a Element
performed on the elements of an ConcreteVisitor
set of objects interact. Promotes loose +accept(in v : Visitor)
object structure. Lets you define a
coupling by keeping objects from referring
new operation without changing +visitElementA(in a : ConcreteElementA)
to each other explicitly and it lets you vary
updates the classes of the elements on +visitElementB(in b : ConcreteElementB)
their interactions independently.
which it operates.
ConcreteMediator ConcreteColleague
ConcreteElementA
ConcreteElementB
+accept(in v : Visitor)
+accept(in v : Visitor)
Copyright © 2007 Jason S. McDonald Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John (1995). Design Patterns: Elements of
Reusable Object-Oriented Software. Reading, Massachusetts: Addison Wesley Longman, Inc..
http://www.McDonaldLand.info

2. Adapter
«interface»
Proxy Client
Adapter Client
Type: Structural
+operation() Type: Structural
«interface»
What it is: Subject
What it is:
Convert the interface of a class into +request()
Provide a surrogate or placeholder for
another interface clients expect. Lets another object to control access to it.
classes work together that couldn't
ConcreteAdapter
otherwise because of incompatible
Adaptee
interfaces.
-adaptee
+adaptedOperation() represents
RealSubject Proxy
+operation()
+request() +request()
Abstraction Client
Bridge Abstract Factory
+operation()
«interface»
Type: Structural
«interface»
Type: Creational AbstractFactory
Implementor
«interface»
+createProductA()
What it is:
+operationImpl() AbstractProduct
What it is: +createProductB()
Decouple an abstraction from its
Provides an interface for creating
implementation so that the two can vary
families of related or dependent
independently.
objects without specifying their
concrete class.
ConcreteFactory
ConcreteImplementorA ConcreteImplementorB ConcreteProduct
+createProductA()
+operationImpl() +operationImpl() +createProductB()
«interface»
«interface»
Composite Builder
Component Director
Builder
children
+operation()
+construct() +buildPart()
Type: Structural Type: Creational
+add(in c : Composite)
+remove(in c : Composite)
What it is: What it is:
+getChild(in i : int)
Compose objects into tree structures to Separate the construction of a
represent part-whole hierarchies. Lets complex object from its representing
clients treat individual objects and so that the same construction
compositions of objects uniformly. process can create different ConcreteBuilder
Composite representations.
+buildPart()
Leaf +operation() +getResult()
+add(in c : Composite)
+operation()
+remove(in c : Composite)
+getChild(in i : int)
«interface»
Decorator
ConcreteComponent
Factory Method Creator
Component «interface»
+operation() Product
+operation() +factoryMethod()
Type: Structural Type: Creational
+anOperation()
What it is: What it is:
Decorator
Attach additional responsibilities to an Define an interface for creating an
+operation() object dynamically. Provide a flexible object, but let subclasses decide which
alternative to sub-classing for extending class to instantiate. Lets a class defer
functionality. instantiation to subclasses.
ConcreteDecorator
ConcreteCreator
ConcreteProduct
-addedState
+factoryMethod()
+operation()
+addedBehavior()
Client
Facade Prototype
Facade
Complex system
«interface»
Type: Structural Type: Creational
Prototype
+clone()
What it is: What it is:
Provide a unified interface to a set of Specify the kinds of objects to create
interfaces in a subsystem. Defines a high- using a prototypical instance, and
level interface that makes the subsystem create new objects by copying this
easier to use. prototype.
ConcretePrototype1 ConcretePrototype2
+clone() +clone()
«interface»
FlyweightFactory
Flyweight
Flyweight Singleton
+getFlyweight(in key) +operation(in extrinsicState)
Singleton
Type: Creational
Type: Structural
-static uniqueInstance
Client What it is: -singletonData
What it is:
Ensure a class only has one instance and
Use sharing to support large numbers of +static instance()
provide a global point of access to it.
fine grained objects efficiently. +SingletonOperation()
ConcreteFlyweight
-intrinsicState
UnsharedConcreteFlyweight
+operation(in extrinsicState)
-allState
+operation(in extrinsicState) Copyright © 2007 Jason S. McDonald Gamma, Erich; Helm, Richard; Johnson, Ralph; Vlissides, John (1995). Design Patterns: Elements of
Reusable Object-Oriented Software. Reading, Massachusetts: Addison Wesley Longman, Inc..
http://www.McDonaldLand.info