I-DigitalTEK Agile Development IT Solutions for Growing Business XP Programming Code Refactoring I-DigitalTEK K I IdigitalTEK

XP Patterns “ In Software Engineering, a Design Pattern is a general reusable solution to a commonly occurring problem in software design . A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations “ Delegation - one object relying upon another to provide a specified set of functionalities . Aggregation - object may only contain reference or pointer (and not have lifetime responsibility for it) . Consultation - the composite type “has an” object of a simpler type, while in sub-typing, the subtype “is an” instance of its parent type.

“ In Software Engineering, a Design Pattern is a general reusable solution to a commonly occurring problem in software design . A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations “

Delegation - one object relying upon another to provide a specified set of functionalities .

Aggregation - object may only contain reference or pointer (and not have lifetime responsibility for it) .

Consultation - the composite type “has an” object of a simpler type, while in sub-typing, the subtype “is an” instance of its parent type.

Patterns Classification “ Design patterns originally grouped patterns into categories Creational patterns , Structural patterns , and Behavioral patterns , and described them using the previous concepts of delegation , aggregation , and consultation .“ Behavioral - Template, Mediator, Visitor, Iterator, Command, Memento, Observer, State, Strategy, Interpreter, Chain of Responsibility. Structural - Decorator, Composite, Façade, Bridge, Adapter, Flyweight, Proxy. Creational - Singleton, Builder, Prototype, Abstract Factory, Factory Method.

“ Design patterns originally grouped patterns into categories Creational patterns , Structural patterns , and Behavioral patterns , and described them using the previous concepts of delegation , aggregation , and consultation .“

Behavioral - Template, Mediator, Visitor, Iterator, Command, Memento, Observer, State, Strategy, Interpreter, Chain of Responsibility.

Structural - Decorator, Composite, Façade, Bridge, Adapter, Flyweight, Proxy.

Creational - Singleton, Builder, Prototype, Abstract Factory, Factory Method.

XP Patterns Liskov Substitution Principle – “ Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T. “ Open/Closed Principle states " software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification that is, such an entity can allow its behavior to be modified without altering its source code. “ Hint: “ Functions that use pointers or references to base classes must be able to use object of derived classes with out knowing it.” “ No Class should derive from a concrete class.”

Liskov Substitution Principle – “ Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T. “

Open/Closed Principle states " software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification that is, such an entity can allow its behavior to be modified without altering its source code. “

Hint:

“ Functions that use pointers or references to base classes must be able to use object of derived classes with out knowing it.”

“ No Class should derive from a concrete class.”

XP Patterns Behavioral Strategy - Encapsulates a family of algorithms so that they vary independently of the client that instantiate it and allow for interchangeability Observer - One-to-many relationship across objects that allow to notify dependencies of a change in state of the caller automatically’ State - Behavior is altered when its internal state changes. A class that encapsulate the state of an object. Hint: “ Design to an interface, not an implementation” “ Separate what varies from what stay the same”

Strategy - Encapsulates a family of algorithms so that they vary independently of the client that instantiate it and allow for interchangeability

Observer - One-to-many relationship across objects that allow to notify dependencies of a change in state of the caller automatically’

State - Behavior is altered when its internal state changes. A class that encapsulate the state of an object.

Hint:

“ Design to an interface, not an implementation”

“ Separate what varies from what stay the same”

XP Patterns Behavioral Template Method - let subclasses redefine a base algorithm without changing its structure and use delegation to decide which behavior to call. Iterator - access aggregate object s sequentially . Visitor - Add capabilities to composite. Mediator - centralized control logic and communications. Hint: “ A class should have only one reason to change.” “ Encapsulate what varies.”

Template Method - let subclasses redefine a base algorithm without changing its structure and use delegation to decide which behavior to call.

Iterator - access aggregate object s sequentially .

Visitor - Add capabilities to composite.

Mediator - centralized control logic and communications.

Hint:

“ A class should have only one reason to change.”

“ Encapsulate what varies.”

XP Patterns Behavioral Command - support undoable operation and encapsulates request as object so that they can be passed as parameters to create distinct functionality. Memento - "undo" and return object to previous state. Chain Of Responsibility - handle request with more than one object. Hint: “ No Class should derive from a concrete class.” “ No Method should override an implemented method of its base class.”

Command - support undoable operation and encapsulates request as object so that they can be passed as parameters to create distinct functionality.

Memento - "undo" and return object to previous state.

Chain Of Responsibility - handle request with more than one object.

Hint:

“ No Class should derive from a concrete class.”

“ No Method should override an implemented method of its base class.”

XP Patterns Structural Adapter - converts interface that were incompatible otherwise. Façade - unified a set of interfaces to create subsystem. Decorator – adding additional responsibilities or functionalities to an object dynamically is a flexible alternative to sub-classing and aggregation. Composite - structure that treats tree element s as individual objects. Hint: “ Simplify interfaces.”

Adapter - converts interface that were incompatible otherwise.

Façade - unified a set of interfaces to create subsystem.

Decorator – adding additional responsibilities or functionalities to an object dynamically is a flexible alternative to sub-classing and aggregation.

Composite - structure that treats tree element s as individual objects.

Hint:

“ Simplify interfaces.”

XP Patterns Structural Bridge - Decouples implementation from interfaces. Flyweight - reduces the number of object instances at runtime and provide many "virtual instances” Proxy - is a representative of an object and act as a place holder. Hint: “ Only talk to your friend.”

Bridge - Decouples implementation from interfaces.

Flyweight - reduces the number of object instances at runtime and provide many "virtual instances”

Proxy - is a representative of an object and act as a place holder.

Hint:

“ Only talk to your friend.”

XP Patterns Creational Factory - binds an object to an interface to allow subclass to decide upon the instantiation. Singleton - Ensure one instance of a class and a global access to it. Interpreter - to add method to a class structure beyond interpretation Hint: “ Classes are about behavior and functionality.”

Factory - binds an object to an interface to allow subclass to decide upon the instantiation.

Singleton - Ensure one instance of a class and a global access to it.

Interpreter - to add method to a class structure beyond interpretation

Hint:

“ Classes are about behavior and functionality.”

XP Patterns Creational Prototype - Generate objects whose type is not known. Builder – to construct a complex object step by step Hint: “ Don’t call us! We will call you.”

Prototype - Generate objects whose type is not known.

Builder – to construct a complex object step by step

Hint:

“ Don’t call us! We will call you.”

Reference Material I-DigitalTek http://www.i-digitaltek.net “ Head First Design Patterns ” 2004 ISBN 10: 0-596-00712-4

I-DigitalTek http://www.i-digitaltek.net

“ Head First Design Patterns ” 2004 ISBN 10: 0-596-00712-4