Clean Code

Question 1

What are Lehman’s two laws?

Answer 1

A system that is used will be changed.
An evolving system increases its complexity unless work is done to reduce it.

Question 2

What are the SOLID principles?

Answer 2

Single Responsibility
Open Closed
Liskov Substitution
Interface Segregation
Dependency Inversion

Question 3

What does the Single Responsibility principle say?

Answer 3

A module should only have a single responsibility
Violation: class Report parses and visualizes report
Solution: split class into Parser and Visualizer

Question 4

What does the Open Closed Principle say?

Answer 4

Modify behavior by adding new code, not by changing old code
Violation: JPlag-Gen insert strategy hard coded as part of obfuscation method
Solution: use strategy interface, pass implementation

Question 5

What does the Liskov Substitution principle say?

Answer 5

Subclasses must not change behavior of superclass
Violation: subclass Square of Rectangle, setWidth breaks
Solution: interface Shape
Logically: Precondition must be weaker and postcondition stronger

Question 6

What does the Interface Segregation Principle say?

Answer 6

Interfaces should be as lean as possible
Violation: broad interface XeroxJob
Solution: Split into PrintJob, StapleJob, …

Question 7

What does the Dependency Inversion principle say?

Answer 7

Depend upon abstractions, not implementations
Violation: TextEditor depends on Keyboard
Solution: TextEditor depends on Reader, Keyboard implements Reader

Question 8

What are some other Clean Code principles?

Answer 8

Law of Demeter
Boy Scout Rule
Principle of Least Surprise
Coding Conventions
Don’t Repeat Yourself
Keep it simple, stupid
You ain’t gonna need it
Single level of abstraction