Chair of Software Engineering
Code Review
Exercise Session
1
Reviews
• Review: examination of (software) artifacts, in
order to find mistakes and improve the quality
of the artifact
• Examples for artifacts
– Source Code
– Design Documents (SRS Doc, API-Design Doc)
2
Purpose of code reviews
• Ensure that code has sufficient quality to be
released / committed
– Review formatting / documentation of code
– Review code correctness and efficiency
• Teach (new) developers how to improve code
w.r.t.
– Code quality
– Consistency
– Maintainability
3
Why review?
• Reviewing is effective to find mistakes
• Developers (hopefully) write better code
when others will look at it
– “You don‘t want to be the guy with the ugly
code...“
4
Effectiveness of Reviews
• Inspection of design & code [Fagan 1976]
– 67% - 82% of all faults were found by inspections
– 25% time saved on programmer resources (despite inspections)
• [Fagan 1986]
– 93% of all faults were found by inspections
• Cost reduction for fault detection (compared with testing)
– [Acerman+ 1989]: 85%
– [Fowler 1986]: 90%
– [Bush 1990]: 25.000 US$ saved PER inspection
5
How to review?
Many different approaches, e.g.
• Personal review
– Author reviews her own code Not objective,
but available to every developer
• Over-the-shoulder
– Other developer looks „over the shoulder“ of the
code author; read / discuss code together
6
How to review?
Many different approaches (continued)
• Walkthroughs
– Scheduled meeting, chaired by a moderator
– Participants prepare for the meeting in advance
– Author presents and provides information
• Advantage: author knows the code best
• Disadvantage: author might feel attacked personally; tries to defend
the code
• Inspections (more formal than walkthroughs)
– Code presenter different from code author (author is present
but has passive role; only answers specific questions)
– Stronger focus on specific aspects (checklist approach)
Result of reviews: Review Report (protocoll of the meeting,
records all errors found) 7
Best practices
• Restrict to review to max. 60 – 90 min
– Reviewers performance in finding defects drops
after that time span as human concentration
declines
• Review fewer than 200 - 400 LOC/hour
– With more LOC, the ability to find defects
diminishes
– Reviewing needs time if code should be fully
understood by reviewers
8
Best practices
• Authors should prepare the source code for
review
– Format and document code
– Put special review- comments on sections which
should be reviewed in in-depth
• Establish quantifiable goals for code review
and capture metrics so you can improve your
process
9
Best practices
• Use checklists for authors and reviewers
– Helps to limit discussion and focus on important aspects
• Verify that defects are actually fixed
– Follow up on the Review Report produced in the last meeting
• Create a good code review culture in which finding defects
is viewed positively
– Review the product, not the producer
– Ask questions instead of making accusations
– Stick to the review agenda
– Raise issues, don‘t resolve them
– Limit discussions
– Stick to technical correctness; avoid style discussions
10
What to review
Include sections... Omit sections...
• of complicated logic • which are
• where defects severely „straightforward“ (no
damage essential system complications)
capability • of a type already
• dealing with new reviewed by the team in a
environments similar past project
• designed by new or • that, if faulty, are not
inexperienced team expected to effect
members functionality
• Reused code
• Repeated parts of code
11
Summary
• Very effective techniques to ensure higher
quality of code (and other software artifacts)
• Low technology (“paper and pencil”)
– Many supporting tools are available
(search for them)
• Use reviews in your own projects
12
Sources
Slides based on material from:
• G. Engels; Slides: Software Quality Assurance – Chapter V; University of Paderborn;
2008; http://is.uni-paderborn.de/fachgebiete/fg-engels/lehre/ss08/software-
quality-assurance/lecture-notes.html
• SmartBear Software; White Paper; 11 Best Practices for Peer Code Review;
http://www.smartbear.com/PDF/11_Best_Practices_for_Peer_Code_Review.pdf
• *Ackerman+1989+ A.F. Ackerman, L.S. Buchwald, F.H. Lewski, “Software inspections:
an effective verification process”, IEEE Software 6 (May 1989), pp. 31-36
• *Bush 1990+ M. Bush, “Improving software quality: the use of formal inspections at
Jet Propulsion laboratory” Proceedings of the 12th International Conference on
Software Engineering, Nice, France, March 1990, pp. 196-199
• *Fowler 1986+ P.J. Fowler, “In-process inspections of workproducts at AT&T”, AT&T
Technical Journal 65 (March/April 1986), pp. 102-112
• *Fagan 1976+ M.E. Fagan, “Design and code inspections to reduce errors in
program development”, IBM Systems Journal 15 (No. 3, 1976), pp. 182-211
• [Fagan 1986+ M.E. Fagan, “Advances in software inspections”, IEEE Transactions on
Software Engineering, SE-12 (July 1986), pp. 744-751
13
