ESDST - 2017 (Volume 5 - Issue 05)

Impact of Refactoring on Software Quality

DOI : 10.17577/IJERTCONV5IS05009

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Prabhjot Kaur, Puneet Mittal, 2017, Impact of Refactoring on Software Quality, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH & TECHNOLOGY (IJERT) ESDST – 2017 (Volume 5 – Issue 05),

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Impact of Refactoring on Software Quality

Prabhjot Kaur

Computer Science and Engg. Department Punjab Technical University

Jalandhar, India

Puneet Mittal

Computer Science and Engg. Department Baba Banda Singh Bahadur Engineering College

Fatehgarh Sahib, India

Abstract Refactoring is the process of transformation of software. It changes its internal structure of software without affecting its external behavior. Bad smells means there are potential problems in the code, which we have to refactor. In this paper, we use two tools for bad smells detection on object oriented open source software are PMD and JDeodrant. Then after refactoring bad smells, we analyze the impact of refactoring on external quality attribute of software.

Keywords Refactoring, Metrics, Quality of Software

  1. INTRODUCTION

    1. Refactoring

      Refactoring code is the process of reorganizing code with the intent of simplifying both design and structure while not changing the functionality of the code [4]. By refactoring, we makes the code clean. It enhances the quality of software by removing potential problem in code. It minimizes the chances of introducing of bugs in the code.

    2. Bad Smells

      Bad smells are the defect in design of the software. Code smells are called as Bad smell. It is an indication of flaws in code which to be removed by applying appropriate refactoring technique. Fowler [16] given 22 bad smells and their respective 72 refactoring techniques to remove these bad smells. There are various tools to detect the bad smells. We detect 6 bad smells in the code. JDeodrant tool will detect 4 bad smells are- God class, Long method, Feature envy and Type Checking. Bad smell detected by PMD are- Dead code and Long parameters list.

      • God Class- means a large class. Too many functions in one class so its difficult to understand functionality of class.

      • Long Method-means very long method in a class.

      • Feature envy-means a class that is more interested to use function or methods of another class.

      • Type Checking-it is switch statement bad smell. It has more duplication of code. So it is best to use polymorphism instead of switch statements.

      • Dead Code- means variable, methods and classes that does not perform any functionality in software.

      • Long Parameter List-means too many parameters are passed in parameter List.

    3. Refactoring Techniques

      Technique used for refactor the bad smells are called as Refactoring Techniques. These are the set of procedures to remove bad smell or clean the code. There are some refactoring techniques [16] used are-

      • Extract Method – means extracting the set of statements into a new method.

      • Extract Class means extracting the set of methods and statements into a new class from the old class.

      • Move Method means methods from one class to another more relevant class.

      • Remove or Delete means delete the unused imports, local variables, unused private methods.

      • Replace Conditional with Polymorphism- means replace switch conditional statements with polymorphism.

      • Introduce Parameter Objectmeans replace parameter with an object.

      • Replace Parameter with Method Call means replace parameter passing function with value getting code inside the class.

    4. Tools Used

      • Eclipse- It is an Java based open source Integrated Development platform. It is designed in such a way that it can be extensible using plugins. It supports various languages C, C++, JAVA, PHP and COBOL. We can integrate bad smell detection plugins and refactoring tools into eclipse for refactoring the code.

      • JDeodrant Plugin- is an eclipse plugin which are used for detecting and removing bad smells in the code. It can detect four bad smells are Feature envy, God Class, Type Checking and Long Method. It detects bad smells in java based code.

      • PMD Plugin-is a static java source analyze. It can be integrated into eclipse as a plugin. It can detect bad smells are- Dead code, Long Parameter List and Duplication Code.

      • Metrics 1.3.6 Plugin- is a quality calculation tool. It can calculates No. of attributes, Lines of code, No. of classes, Weighted methods per Class, Cohesion and Coupling.

    5. Quality Attributes

      Software Quality Attributes are the characteristics of software by which quality is described and evaluated. It is divided into two groups- Internal Quality Attributes and External Quality Attributes. Internal Quality is measured directly from the

      code. External quality attributes are measured with the help of internal quality attributes.

      Internal Quality Attributes are-

      • Lack of Cohesion

      • Coupling

      • Depth of Inheritance

      • Number of Classes

      • Lines of Codes

      • Weighted Method per Class

      • Abstractness

        External Quality Attributes are-

      • Understandability

      • Reusability

      • Functionality

      • Effectiveness

      • Flexibility

      • Extendibility

  2. LITERATURE SURVEY

    Fowler et al. [16] describes the 22 bad smells and their 72 respective techniques to refactor bad smells. They mention duplicate code as a serious kind of bad smell. It increases maintenance cost of software. Due to increasing use of open source software and its variants, there is also increased use of code reuse. Due to Code reuse, it results in duplication of code.

    Bansiya and Davis [10] presented a QMOOD (Quality Model for Object Oriented Designed) that access quality attributes like reusability, functionality, extendibility, flexibility, understandability, effectiveness. QMOOD relates low level design properties such as encapsulation, coupling and cohesion to high level quality attributes. It weighted quality attributes accordance to their influence and importance in the system.

    Alshayed [1] investigate the effect of refactoring on software quality attributes. He focused on quality attributes like adaptability, maintainability, understandability, reusability and testability. They apply refactoring on three open source software- UML tool, terpPaint, Rabtpad. But after refactoring, he concludes that it does not necessary that refactoring improve the quality attributes of software.

    Kannangara and Wijayanaka [21] investigate the impact of refactoring on internal quality attributes are maintainability, DIT, LOC, coupling. They compare quality attributes of nonrefactored code with refactored code. After study, they get result that only maintainability is improve, other attributes does not show any positive effect.

    External Quality Attributes

    C. Internal Quality Attributes

    TABLE II. shows the internal quality attributes formula used for calculation

    Tsantalis et al. [15] presented a tool, JDeodrant which is implemented as a plugin in Eclipse that automatically indentifies God class. They remove these smells by extract class refactoring. They also indentify the application of extract class refactoring in bad smells removal. Kaur and Kaur [14] provide a review on bad smell detection tool PMD and JDeodrant using eclipse. They discuss and compare the bad smell detected by PMD and JDeodrant and their refactoring. They apply refactoring techniques on Online Exam System which is written in java.

    They refactor 6 bad smells using tools.

  3. PROBLEM FORMULTION

    To maintain the poorly design system is difficult and tough work. Software goes through various evolutionary development lifecycle, and then its quality attributes degrade. So it becomes difficult for developer to maintain the understandability, extensibility and reusability of the software. So refactoring is a way to maintain overall functionality and behavior of the system. So we proposed to detect the bad smells in object oriented open source java software and remove these by refactoring techniques. Then after refactoring, we analyze the impact of refactoring on external quality attributes of the software.

      • To find different bad smells in an open source softwares.

      • To analyze various refactoring techniques.

      • To clean code by removing these bad smells through refactoring.

      • To analyze the impact of refactoring on software quality before and after refactoring.

  4. RESEARCH METHOLOGY

    1. Methodology

      JDeodrant and PMD are bad smells detector. Object oriented open source software are JChart 2D (3.2.1),GhantProject(9.11) and RabtPad(0.1).

      1. Measure internal quality attributes of the software.

      2. Detect code bad smell by using PMD and JDeodrant tools in the software.

        1. Indentify the type of bad smell detected.

        2. Indentify location of bad smell detected.

        3. Refactoring techniques to be applied to it to refactor bad smell.

        4. Check, is there any error occur during refactoring, if not then move to next step to find next bad smell, otherwise rollback refactoring and applied another refactoring technique to refactor bad smell.

      3. Then after removing bad smells in the codes, measure the internal quality attributes of software.

      4. Calculates the external quality attributes of software with the help of internal quality attributes. Compare the external quality attributes of software before and after refactoring to analyze the impact of refactoring.

    2. External Quality Attributes.and Internal Qualiy Attributes

    External QA

    Formula Used for Calculation

    Reusability

    -0.25*Coupling+0.25*Cohesion+0.5* Messaging+

    0.5*Design Size.

    Flexibility

    0.25*Encapsulation – 0.25*Coupling + 0.5*Composition +

    0.5* Polymorphism.

    Understand- ability

    -0.33*Abstraction+0.33*Encapsulation-

    0.33*Coupling+0.33* Cohesion-0.33*Polymorphism- 0.33*Complexity-0.33*Design Size.

    Functionality

    0.12*Cohesion + 0.22*Polymorphism + 0.22*Messaging + 0.22*Design Size +0.22*Hierarchies.

    Extendibility

    0.5*Abstraction – 0.5*Coupling + 0.5*Inheritance +0.5* Polymorphism.

    Effectiveness

    0.2*Abstraction + 0.2*Encapsulation + 0.2*Composition+

    0.2* Inheritance+ 0.2*Polymorphism.

    TABLE I. Shows the external quality attributes given by bansiya[12]

    TABLE III. Shows the Intenal Quality Formula

    Design

    Property

    Metrics used by Bansiya

    Metrics we Used

    Design Size

    Design Size in Classes (DSC)

    Number of Classes

    Hierarchies

    Number of Hierarchies (NOH)

    Depth of Inheritance

    Tree

    Abstraction

    Average Number of Ancestors

    (ANA)

    Abstractness

    Encapsulation

    Data Access Metrics (DAM)

    (Total no. of attributes

    static Attributes) / (Total no. of attributes

    + static Attributes)

    Coupling

    Direct Class Coupling (DCC)

    Instability

    Cohesion

    Cohesion Among Methods of Classes(CAM)

    1/Lack of Cohesion of Methods

    Composition

    Measure of Aggregation

    (MOA)

    Number of Overridden

    Methods

    Inheritance

    Measure of Functional Abstraction (MFA)

    No. of Overridden

    Methods /Number of Methods

    Polymorphism

    Measure of Polymorphic Methods (NOP)

    Number of Overridden Methods

    Messaging

    Class Interface Size (CIS)

    Number of Methods

    Complexity

    Number of Methods (NOM)

    Weighted Methods per

    Class

  5. RESULTS

    Number of bad smells detected is shown in table IV. Table V and table VI shows the internal quality attributes before and after refactoring respectively. Then table V and table VI shows the external quality attributes values before and after refactoring respectively.

    TABLE IV. Show the number of bad smell detected in software

    Bad smells

    RabtPad

    JChart2D

    GhanttProject

    God Class

    10

    8

    33

    Feature envy

    5

    9

    34

    Long method

    27

    16

    150

    Type Checking

    6

    –

    6

    Dead Code

    31

    5

    70

    Long Parameter List

    –

    2

    3

    TABLE V. Shows Internal Quality Attributes of Software Before Refactoring

    Softwares Metrics

    RabtPad

    JChart2D

    Ghantt Project

    Coupling

    0.252

    0.406

    0.397

    Cohesion

    2.551

    2.463

    0.2595

    Messaging

    7.581

    3.991

    6.189

    Design Size

    1.824

    9.727

    9.211

    Encapsulation

    0.4819

    0.1797

    0.5288

    Composition

    8.581

    1.411

    4.709

    Polymorphism

    0.258

    0.467

    0.417

    Abstraction

    0.044

    0.0851

    0.206

    McCabe Complexity

    18.871

    8.533

    15.034

    Inheritance

    0.966

    0.882

    0.937

    Hierarchies

    2.744

    3.636

    2.166

    TABLE VI. Shows Internal Quality Attributes of Software After Refactoring

    td>

    Abstraction

    Softwares

    Metrics

    RabtPad

    JChart2D

    Ghantt Project

    Coupling

    0.296

    0.623

    0.397

    Cohesion

    3.164

    2.898

    0.2595

    Messaging

    10.12

    4.236

    6.189

    Design Size

    2.941

    12.727

    9.211

    Encapsulation

    0.4903

    0.337

    0.5288

    Composition

    5.38

    1.543

    4.709

    Polymorphism

    0.34

    0.350

    0.417

    0.077

    0.0865

    0.206

    McCabe Complexity

    17.44

    7.786

    15.034

    Inheritance

    0.967

    0.9174

    0.937

    Hierarchies

    2.18

    3.043

    2.166

    TABLE VII. Shows External Quality Attributes of Software Before Refactoring

    External Quality Attributes

    RabtPad

    JChart2D

    GhanttProject

    Reusability

    5.277

    7.373

    7.665

    Flexibility

    4.476

    0.882

    2.595

    Understandability

    -6.011

    -5.469

    -8.077

    Functionality

    3.042

    4.216

    3.987

    Extendibility

    0.508

    0.514

    0.581

    Effectiveness

    2.066

    0.604

    1.359

    TABLE VIII. Shows External Quality Attributes of Software After Refactoring

    External Quality Attribute

    RabtPad

    JChart2D

    GhanttProject

    Reusability

    7.247()

    9.050()

    11.431()

    Flexibility

    2.908()

    0.875()

    1.731()

    Understandability

    -5.755()

    -6.051(

    -7.469()

    Functionality

    3.807()

    4.826()

    5.710()

    Extendibility

    0.544()

    0.365()

    0.662()

    Effectiveness

    1.450()

    0.646()

    1.000()

    Fig. 1. Shows External Quality Attributes of RabtPad before Refactoring and after Refactoring.

    Fig. 2. Shows External Quality Attributes of JChart2D before Refactoring and after Refactoring.

    Fig. 3. Shows External Quality Attributes of GhanttProject before Refactoring and after Refactoring.

  6. CONCLUSION

In this paper, we notice the impact of refactoring of refactoring on external and internal quality attributes. It shows that reusability and functionality of all three shows an postive impact. But other external attributes like extendibility, understandability and flexibility shows negative impact on software after refactoring. So conclude from the experiment that group of refactoring techniques have postive and negative impact on software.

In future work, we can detect more bad smells and then apply more refactoring techniques to software to refactor these smells in a code. Then, after refactoring analyze the impact on quality.We can also check impact of refactoring on other quality attributes like testability.

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