Code Smell Research: History and Future Directions Second PLOW Installment - March 5, Nikolaos Tsantalis Computer Science & Software Engineering

Changes aiming to improve the future maintainability and reliability of the software system. Second PLOW Installment - March 5, 20142

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Refactoring Object-oriented Frameworks, University of Illinois at Urbana-Champaign – Introduced the concept of refactorings as behavior- preserving program restructuring operations. – Introduced the concept of preconditions as conditions that should be examined to determine whether a refactoring can be applied safely. Second PLOW Installment - March 5, 20144

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Duplicated Code: “If you see the same code structure in more than one place, … find a way to unify them.” Second PLOW Installment - March 5, 20146

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Second PLOW Installment - March 5,

Code smell definition for Inappropriate Interface inappropriateInterface(?class,?interface,?subclasses) :- findall(, commonSubclassInterface(?class,?itf,?scs), ?result), removeDuplicates(?result,?nodups), member(,?nodups) Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Treat the improvement of object-oriented design as a search problem in the space of alternative designs The move in the search space is achieved by modeling refactorings ( inheritance-related ) Apply search algorithms using QMOOD as the fitness function ( rank alternative designs ) The outcome is a sequence of refactorings leading to the optimal design Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Many code smell definitions are based on historical change information – Shotgun Surgery: When every time you make a kind of change, you have to make a lot of little changes to a lot of different classes. – Parallel Inheritance Hierarchies: When every time you make a subclass of one class, you also have to make a subclass of another. Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

12 code smells 6 Professional developers were hired to implement change requests 4 medium-sized Java systems with known code smells 4 weeks of development Daily interviews and think-aloud sessions Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5, LIMITATION

Advantages: Feasible and behavior preserving solutions to design problems Ranking and prioritizing solutions based on their expected effect on design quality A holistic approach for preventive maintenance Second PLOW Installment - March 5,

1.Identify places where software should be refactored (known as bad smells). 2.Determine which refactoring(s) should be applied to the identified places. 3.Guarantee that the applied refactoring preserves behavior. 4.Apply the refactoring. 5.Assess the effect of the refactoring on quality characteristics of the software. 6.Maintain the consistency between the refactored code and other software artifacts. Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5, doStateA(); if state == STATE_A else if state == STATE_B doStateB();

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5, Since the beginning of 2011 …

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

“Debt” is the effect of incomplete, immature, or inadequate maintenance activities Delayed tasks may bring a short-term benefit ( higher productivity, shorter release time ) Might have to be paid back in the future with “Interest” ( increased effort ) “Principal” is the effort to pay off the debt Second PLOW Installment - March 5,

Tracking clones as project evolves Verifying the consistent modification of clones Updating clones and groups as project evolves Assessing the harmfulness of clones Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

So far, we used – Static source code analysis – Semantic analysis – Change history analysis Second PLOW Installment - March 5,

Second PLOW Installment - March 5,

Every code smell involves a certain risk for future maintainability Second PLOW Installment - March 5,

Likelihood of occurrence of the risky event Exposure of the system to the event Consequence of the event Second PLOW Installment - March 5,

Risky events  changes driven by code smells – Ex. 1: Fixing the same bug in a clone group – Ex. 2: Making a method more “envy” to another class Intuition: code that changes frequently due to a design flaw imposes a high risk to the maintainability of a system Likelihood  proneness to code smell driven changes ( estimated from the history of changes ) Second PLOW Installment - March 5,

Intuition: the more extensively a module is used, the more extensive the propagation of code smell driven changes to dependent modules Exposure  the number and strength of incoming dependencies ( estimated from static and dynamic analysis ) Second PLOW Installment - March 5,

Consequence  cost of code smell driven changes (effort, time, money). From the opposite perspective: Consequence  effect of removing the code smell. Estimated by computing the impact of the corresponding refactoring on metrics. Second PLOW Installment - March 5,

Given a set of different types of refactoring opportunities in a software system Conflicts Dependencies Second PLOW Installment - March 5,

Second PLOW Installment - March 5,