Design Patterns

Design Patterns

By Mareck Kortylevitch and

By Mareck Kortylevitch and

Piotreck Ratchinsky

Piotreck Ratchinsky

What is Design Pattern?

What is Design Pattern?



Recurring solution to known

Recurring solution to known

problems

problems



Workaround to problems

Workaround to problems

that arise when developing

that arise when developing

software within a particular

software within a particular

context

context

History

History



Precursor of design pattern

Precursor of design pattern

was Christopher Alexander

was Christopher Alexander



First Design Patterns used in

First Design Patterns used in

architecture

architecture

Why to use DP?

Why to use DP?



Help you learn from others'

Help you learn from others'

successes instead of your

successes instead of your

own failures

own failures



Provide a communication

Provide a communication

platform concerning

platform concerning

elegant, reusable solutions

elegant, reusable solutions

to commonly encountered

to commonly encountered

programming challenges

programming challenges

Why to use...continuation

Why to use...continuation



Enforce using techspeak

Enforce using techspeak



Isolate changes in the code

Isolate changes in the code



Design and interaction of

Design and interaction of

objects

objects

Design Patterns Examples

Design Patterns Examples



Facade

Facade



Adapter

Adapter



Singleton

Singleton



Abstract Factory

Abstract Factory



Bridge

Bridge

Facade - definition

Facade - definition



Provide a unified interface

Provide a unified interface

to a set of interfaces in a

to a set of interfaces in a

subsystem. Façade defines a

subsystem. Façade defines a

higher-level interface that

higher-level interface that

makes the subsystem easier

makes the subsystem easier

to use.

to use.

Facade -

Facade -

UML class

UML class

diagram

diagram

Facade - example

Facade - example



Facade

Facade

  

  

(MortgageApplication)

(MortgageApplication)



knows which subsystem classes are

knows which subsystem classes are

responsible for a request.

responsible for a request.



delegates client requests to

delegates client requests to

appropriate subsystem objects.

appropriate subsystem objects.



Subsystem classes

Subsystem classes

  

  

(Bank,

(Bank,

Credit, Loan)

Credit, Loan)



implement subsystem functionality.

implement subsystem functionality.



handle work assigned by the Facade

handle work assigned by the Facade

object.

object.



have no knowledge of the facade

have no knowledge of the facade

and keep no reference to it.

and keep no reference to it.

Facade – example diagram

Facade – example diagram

Facade

Subsystems

Loan

Credit

Bank

Singleton - definition

Singleton - definition



ensure a class has only one

ensure a class has only one

instance and provide a global

instance and provide a global

point of access to it.

point of access to it.



defines an Instance operation

defines an Instance operation

that lets clients access its unique

that lets clients access its unique

instance. Instance() is a class

instance. Instance() is a class

operation.

operation.



responsible for creating and

responsible for creating and

maintaining its own unique

maintaining its own unique

instance.

instance.

Singleton – UML

Singleton – UML

Singleton

-Singleton()

+static
getInstance():Singleton

-static Singleton: instance