What’s There? What Have We Accomplished?

Rules? Why Rules?

Rules are there to enforce …

  • A working state

  • Maintainability/modifiability (⟶ readability)

  • Respect from …

    • Co-workers

    • Employer

    • Users/customers

Which rules and tools have established in software?

Object Oriented Programming

Talk about the code as if you’d talk about you domain objects.

A rather old discipline …

  • Encapsulation

  • Interfaces

  • Overengineering

  • a hard discipline

Looks like that is part of our craft

  • Not tied to any programming language

  • “This is how things are done”

  • Only a write-up of existing practice

  • Gives things names

  • ⟶ chances are good that what we do is a craft

Coding Style

  • Respect: others might not be as smart as you - they want uniformity

  • No rules?

    • ⟶ consensus is needed

    • People don’t usually consent easily (especially male individuals)

  • All rules?

    • No consensus needed

    • But: rules are never 100% (has your company established prcesses?)

    • War between those who obey the rules and those who (occasionally) don’t

Design Principles: SOLID

  • Single Responsibility

    • Every class must have a single responsibility

  • Open/Closed

    • Software entities must be open for extension, but closed for modification

  • Liskov Substitution

    • It must be possible in a program to exchange two implementations of an interface without compromising the correctness of the program

  • Interface Segregation

    • No client of an interface should be forced to depend on methods it does not use

  • Dependency Inversion

    • High-level modules should not depend on low-level modules. Both should depend on abstractions.

    • Abstractions should not depend upon details. Details should depend upon abstractions.

Antipattern: a pattern that violates any of these principles

Another One: YAGNI

“You ain’t gonna need it!”

  • Extreme Programming (XP)

  • Test Driven Development

  • When everything is covered by tests, then you can implement a feature at the time you need it

  • ⟶ the system can be changed at any time


  • Good architecture allows major decisions to be deferred

  • Maximizes the number of decisions not made

  • Makes choice of tools irrelevant

“Interfaces are a sign of indecisiveness!” 🖕

Project Management: Traditional

  • Road construction business

    • Fundamentally different from software

    • No cycles (version 2.0 of a road?)

  • Hardware manufacturing

    • Somewhere in the middle

    • PCB design

    • BOM

    • Production

    • Bug are fixed ⟶ new version

Project Management: Software

  • Continuous change possible ⟶ happens!

  • Great tools: version control systems (craft?)

  • Do we want continuous change?

    • What is bad about it?

    • Is it necessary?

  • Is it possible to plan 100% ahead?

    • Requiremenets must be rock stable

    • Road construction?

  • Anyway, fact is …

    • Cycles are possible

    • We are too stupid to plan ahead

⟶ let’s just accept the fact, and make the best out of it!

Let’s go AGILE!

So What?

  • Everything’s there: tools, principles, do’s and dont’s …

  • Well understood

  • It’s just that it takes about 20 years to learn all that (because everyone has do experience all that by themselves)

  • Did Bob Martin move anything? (I don’t know.)