Code Quality


  • Characteristics of quality code 
  • Software defects 
  • How to improve code quality 
  • Code quality checking 
  • Coding principles 
  • Commenting

Why we should care Code Quality?

Something to think about

Programs must be written for people to read, and only incidentally for machines to execute

- Abelson and Sussman

Change in Requirements

Change in Requirements

Cost of Defect 

The earlier the better for dealing with defects

Cost of Defect

Software Defects

Software Defect Statistics 

  • Finding, fixing problems in production is 100 times more expensive than during requirements/design phase 
  • 40-50% of typical project work is “avoidable rework” 
  • ~80% of avoidable rework comes from 20% of defects 
  • ~80% of defects come from 20% of modules 
  • ~90% of downtime comes from at most 10% of defects 
  • Peer reviews catch 60% of defects 
  • Perspective-based reviews catch 35% more defects than nondirected reviews (Perspective-based reading is a reading technique that gives each reader a specific viewpoint to use, such as "user" or "tester.") 
  • Disciplined personal practices can reduce defects by up to 75%

But, still...

  • The evidence is overwhelming, but still.. 
  • We never seem to have time to do it, but always seem find time to “redo” it??

What about QA?

  • Can't QA take care of quality? Why should developers care? 
    • Because QA should not care about quality of design and implementation 
    • Instead they should care about “testings that matter”: functionality, acceptance, performance, usability, etc. 
    • Give them a better quality software so they can really focus on “testings that matter”

Technical Debt

  •  “Technical debt” are activities (like refactoring, upgrading a library, conforming to coding standart, ..) that you've left undone 
  • “Technical debt” will hamper your progress if left undone

How to Improve Code (Software) Quality?

Ways to Improve Software Quality

  • Start early 
  • Don't compromise 
  • Schedule time to lower your technical debt 
  • Make it work; make it right (right away) 
  • Requires monitoring and changing behavior 
  • Be willing to help and be helped

Individual Effort

  • Care about quality of your code 
    • Good names for variables, methods, 
    • Short method, smaller classes, 
  • Keep it simple 
  • Write tests with high coverage 
  • Run all your tests before check-in
  • Check in frequently 
  • Ask for feedbacks

Team efforts

  • Avoid shortcuts 
  • Talk collective ownership 
  • team should own the code 
  • Promote positive interaction 
  • Provide constructive feedback 
  • Constant code review

Broken Window Problem 

  • Study shows broken windows lead to vandalism 
  • Code that no one cares for deteriorates quickly 
  • Fix code that is not elegant or looks broken 
  • Keep your code always releasable

Treat Warnings as Errors 

  • Don't say “that's only a warning” 
  • Warnings may have hidden problems 
  • If unavoidable, suppress (selectively)

Strive for Higher Cohesion 

  • Cohesive code is focused, narrow, and small 
    • It does one thing and one thing well
    • Single responsibility principle 
  • Higher cohesion leads to “Lower Cyclomatic Complexity” (Cyclomatic complexity/conditional complexity indicates complexity of a program by providing measurement on the number of linearly independent paths through a program's source code) 
    • Less expensive to maintain 
    • Change in low cohesive code will break something else 
  • Cohesiveness applies to all levels 
    • method, class, component, and subsystem

Code Quality Checking

  • Code Coverage 
  • How much (%) of your code is covered by test? 
  • How about paths through your code? 
  • Is there code that deserve not to be tested? 
  • Code coverage tools can tell you which and how much code is covered 
    • Clover 
    • Cobertura 
    • JaCoCo 
  • Some tools delete code that have no test 
    • Guantanamo 
    • Ashcroft

Cyclomatic Complexity 

  • Cyclomatic Complexity Number (CCN) 
    • Number of distinct paths through code 
  • Strive for lower CCN 
  • Tools can show CCN 
    • PMD 
    • CheckStyle

Code Duplication 

  • Duplicated code is expensive to maintain 
    • Duplicated code is common 
  • Tools that detect code duplication 
    • PMD

Code Analysis 

  • Analyzing code to find bugs
    • Logic errors 
    • Coding guideline violations 
    • Synchronization problems 
    • .. 
  • Tools 
    • PMD 
    • FindBugs 
    • JLint

Coding Principles

  • Simplicity 
  • Clarity 
  • Brevity 
  • Humanity

Commenting Code 

  • Comments should say “Why” or “Purpose” not “How”
  • Don't comment what a code does - I can read the code 
  • Keep it DRY 
  • Don't keep documentation separate from code

Download Course Content