SOLID Principles part 1

SOLID
Single Responsibility Principle
Open/Closed Principle

Dennis van der Stelt Pascal de Jonge
Software Architect Development Lead
Tellus Tellus
http://bloggingabout.net/blogs/dennis/ http://www.pazquality.com/
@dvdstelt @pdejonge
dvdstelt@tellus.com pdejonge@tellus.com

Software Development Network 2013

AGENDA


SOLID
History


Guidance


SOLID
Five principles

Single Responsibility SOLID Open/Closed

Liskov Substitution Interface Seggregation Dependency Inversion

Learn them, love them, live by them…


Software Craftsmanship
is really, really, ridiculously good looking code


SOLID
Books


SOLID
Single Responsibility Principle


SINGLE RESPONSIBILITY PRINCIPLE

there should never be more than
one reason for a class to change



just because you can, doesn’t mean you should



Rules that apply to classes
rule rule same goes for methods,
they should be small which we count by #
01 03 lines
rule rule
they should be smaller how to measure class
02 than that 04 size?

Responsibility : “a reason for change”


Why would we want to separate responsibilities?



Sometimes hard to see…
interface IModem
{
void Dial(string phoneNumber);
void Hangup();
void Send(char c);
char Receive();
}


public interface IConnection
{
void Dial(string phoneNumber);
void Hangup();
}

public interface IDataChannel
{
void Send(char c);
char Receive();
}

public class Modem
{
public Modem(IConnection connection, IDataChannel dataChannel)
{
// ...
}
}



Rule of thumb
If you can’t come up with a
name for your class, it’s probably doing too much!


DEMO
InvoiceCreator


Violation

• God class unneeded complexity
Don’t create
• However
public class OrderService
{
public Order Get(int orderId) { }
public Order Get(string name) { }
public Order Save(Order order) { }
public Order SubmitOrder(Order order) { }
public void CancelOrder(Order order) { }
public void ProcessOrderReturn(int orderId) { }
public void ShipOrder(Order order) { }
}


more classes != more
complex


SOLID
Open/Closed Principle


OPEN/CLOSED PRINCIPLE

software entities should be open for
extension, but closed for
modification


OPEN/CLOSED PRINCIPLE
Non changed code doesn’t need new…


DEMO
Useful patterns


TEMPLATE METHOD PATTERN

AbstractBase class
Program Initialize
SendMessage
Finalize
Execute

EmailSende
r

SendMessage


CONCLUSION

Single Responsibility SOLID Open/Closed

Liskov Substitution Interface Seggregation Dependency Inversion


Thank you
questions?

Dennis van der Stelt Pascal de Jonge
Software Architect Development Lead
Tellus Tellus
http://bloggingabout.net/blogs/dennis/ http://www.pazquality.com/
@dvdstelt @pdejonge
dvdstelt@tellus.com pdejonge@tellus.com

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SOLID Principles part 1

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