Automated refactoring to the Strategy design pattern

ContextThe automated identification of code fragments characterized by common design flaws (or “code smells”) that can be handled through refactoring, fosters refactoring activities, especially in large code bases where multiple developers are engaged without a detailed view on the whole system. Automated refactoring to design patterns enables significant contributions to design quality even from developers with little experience on the use of the required patterns.ObjectiveThis work targets the automated identification of refactoring opportunities to the Strategy design pattern and the elimination through polymorphism of respective “code smells” that are related to extensive use of complex conditional statements.MethodAn algorithm is introduced for the automated identification of refactoring opportunities to the Strategy design pattern. Suggested refactorings comprise conditional statements that are characterized by analogies to the Strategy design pattern, in terms of the purpose and selection mode of strategies. Moreover, this work specifies the procedure for refactoring to Strategy the identified conditional statements. For special cases of these statements, a technique is proposed for total replacement of conditional logic with method calls of appropriate concrete Strategy instances. The identification algorithm and the refactoring procedure are implemented and integrated in the JDeodorant Eclipse plug-in. The method is evaluated on a set of Java projects, in terms of quality of the suggested refactorings and run-time efficiency. The relevance of the identified refactoring opportunities is verified by expert software engineers.ResultsThe identification algorithm recalled, from the projects used during evaluation, many of the refactoring candidates that were identified by the expert software engineers. Its execution time on projects of varying size confirmed the run-time efficiency of this method.ConclusionThe proposed method for automated refactoring to Strategy contributes to simplification of conditional statements. Moreover, it enhances system extensibility through the Strategy design pattern.     

Investigating the evolution of code smells in object-oriented systems

Software design problems are known and perceived under many different terms, such as code smells, flaws, non-compliance to design principles, violation of heuristics, excessive metric values and anti-patterns, signifying the importance of handling them in the construction and maintenance of software. Once a design problem is identified, it can be removed by applying an appropriate refactoring, improving in most cases several aspects of quality such as maintainability, comprehensibility and reusability. This paper, taking advantage of recent advances and tools in the identification of non-trivial code smells, explores the presence and evolution of such problems by analyzing past versions of code. Several interesting questions can be investigated such as whether the number of problems increases with the passage of software generations, whether problems vanish by time or only by targeted human intervention, whether code smells occur in the course of evolution of a module or exist right from the beginning and whether refactorings targeting at smell removal are frequent. In contrast to previous studies that investigate the application of refactorings in the history of a software project, we attempt to analyze the evolution from the point of view of the problems themselves. To this end, we classify smell evolution patterns distinguishing deliberate maintenance activities from the removal of design problems as a side effect of software evolution. Results are discussed for two open-source systems and four code smells.     

代码缺陷与代码味道的自动探测与优化研究

为了实现代码缺陷与代码味道的自动探测与优化, 提升优化与重构的效率, 设计并开发了一套名为SCORT的源代码优化与重构工具。SCORT将源代码解析为抽象语法树, 再探测其中存在的代码缺陷和代码味道, 最后对缺陷和味道进行自动优化和重构。在SCORT中已经实现了对15种常见代码缺陷和六种常见代码味道的检测以及自动优化与重构, 提供了多种代码味道的自动重构算法, 且具有良好的可扩展性。通过对三个待测项目的探测和优化实验结果表明, 对于常见代码缺陷的探测和优化, SCORT的精确率、召回率和准确率均可达100%; 对于部分常见的代码味道, SCORT尚需进一步完善。SCORT有助于开发人员提高代码质量, 减少源代码中存在的缺陷和味道。     

Exception handling refactorings: Directed by goals and driven by bug fixing

Exception handling design can improve robustness, which is an important quality attribute of software. However, exception handling design remains one of the less understood and considered parts in software development. In addition, like most software design problems, even if developers are requested to design with exception handling beforehand, it is very difficult to get the right design at the first shot. Therefore, improving exception handling design after software is constructed is necessary. This paper applies refactoring to incrementally improve exception handling design. We first establish four exception handling goals to stage the refactoring actions. Next, we introduce exception handling smells that hinder the achievement of the goals and propose exception handling refactorings to eliminate the smells. We suggest exception handling refactoring is best driven by bug fixing because it provides measurable quality improvement results that explicitly reveal the benefits of refactoring. We conduct a case study with the proposed refactorings on a real world banking application and provide a cost-effectiveness analysis. The result shows that our approach can effectively improve exception handling design, enhance software robustness, and save maintenance cost. Our approach simplifies the process of applying big exception handling refactoring by dividing the process into clearly defined intermediate milestones that are easily exercised and verified. The approach can be applied in general software development and in legacy system maintenance.     

Identifying refactoring opportunities in object-oriented code: A systematic literature review

ContextIdentifying refactoring opportunities in object-oriented code is an important stage that precedes the actual refactoring process. Several techniques have been proposed in the literature to identify opportunities for various refactoring activities.ObjectiveThis paper provides a systematic literature review of existing studies identifying opportunities for code refactoring activities.MethodWe performed an automatic search of the relevant digital libraries for potentially relevant studies published through the end of 2013, performed pilot and author-based searches, and selected 47 primary studies (PSs) based on inclusion and exclusion criteria. The PSs were analyzed based on a number of criteria, including the refactoring activities, the approaches to refactoring opportunity identification, the empirical evaluation approaches, and the data sets used.ResultsThe results indicate that research in the area of identifying refactoring opportunities is highly active. Most of the studies have been performed by academic researchers using nonindustrial data sets. Extract Class and Move Method were found to be the most frequently considered refactoring activities. The results show that researchers use six primary existing approaches to identify refactoring opportunities and six approaches to empirically evaluate the identification techniques. Most of the systems used in the evaluation process were open-source, which helps to make the studies repeatable. However, a relatively high percentage of the data sets used in the empirical evaluations were small, which limits the generality of the results.ConclusionsIt would be beneficial to perform further studies that consider more refactoring activities, involve researchers from industry, and use large-scale and industrial-based systems.     

An exploratory study on cooccurrence of design patterns and bad smells using software metrics

A design pattern is a general reusable solution to commonly recurring problems in software projects. Bad smells are symptoms existing in the source code that possibly indicate the presence of a structural problem that requires code refactoring. Although design pattern and bad smells be different concepts, literature has shown that they may be related and cooccur during the evolution of a software system. This paper presents an empirical study that investigates cooccurrences of design patterns and bad smells as well as identifies the main factors that contribute to the emergence of the relationship between them. We carried out a case study with five Java systems to: (1) investigate if the use of design pattern reduces bad smell occurrence, (2) identify cooccurrences of design patterns and bad smells, and (3) identify situations that contribute for the cooccurrence emergence. As the main result, we found that the application of design pattern not necessarily avoid bad smell occurrences. The results also show that some design patterns such as composite, factory method, and singleton, are intrinsically modular and might be useful in creating high-quality systems. However, other design patterns such as adapter-command, proxy, and state-strategy, have presented high cooccurrence frequency with bad smells; therefore, they require attention in their implementation. Finally, via manual inspection in the components with cooccurrence, we found that the identified cooccurrences appeared due to poor planning and inadequate application of design patterns.     

代码坏味对软件演化影响的实证研究

代码坏味是指程序设计中存在的不良设计模式或设计缺陷.坏味的存在,被认为会阻碍软件的演化与维护.近年来,研究人员致力于探究坏味产生的影响以及坏味与软件演化之间的关系.已有研究表明,代码坏味会随着软件的演化而不断发生变化.通常,软件的演化将涉及源文件的增加、修改与删除这3类具体操作,了解代码坏味与软件演化中源文件操作的关系,将有助于开发者更好地计划软件开发过程和重构软件代码.因此,针对13种常见的坏味,在8个Java项目共计104个版本中进行了系统的实证研究.研究发现,随着软件版本的演化,含代码坏味的文件在整个项目中的占比在不同的项目中呈现出不同的特征.另外,包含代码坏味的文件更倾向于被修改,而坏味本身与文件的添加或者删除并没有太大的关联.更进一步地,在探究的所有坏味中,有几种特定的坏味对文件的修改产生了显著的影响,且这些坏味文件间存在着明显的重叠.这些发现有助于开发人员更好地了解代码坏味,以便于更好地对软件进行维护.     

Identification of Move Method Refactoring Opportunities

Placement of attributes/methods within classes in an object-oriented system is usually guided by conceptual criteria and aided by appropriate metrics. Moving state and behavior between classes can help reduce coupling and increase cohesion, but it is nontrivial to identify where such refactorings should be applied. In this paper, we propose a methodology for the identification of Move Method refactoring opportunities that constitute a way for solving many common Feature Envy bad smells. An algorithm that employs the notion of distance between system entities (attributes/methods) and classes extracts a list of behavior-preserving refactorings based on the examination of a set of preconditions. In practice, a software system may exhibit such problems in many different places. Therefore, our approach measures the effect of all refactoring suggestions based on a novel Entity Placement metric that quantifies how well entities have been placed in system classes. The proposed methodology can be regarded as a semi-automatic approach since the designer will eventually decide whether a suggested refactoring should be applied or not based on conceptual or other design quality criteria. The evaluation of the proposed approach has been performed considering qualitative, metric, conceptual, and efficiency aspects of the suggested refactorings in a number of open-source projects.     

类间结构型代码味道自动检测的研究

软件重构是改造软件遗留系统、软件重用的重要手段。代码味道用于描述软件设计缺陷,检测代码味道是软件重构的重要步骤。按照代码味道的特征给代码味道分类,对引发重构的主要缺陷――类之间结构型代码味道,给出了自动化检测的原理,设计和实现了一个检测工具。     

Assessing the capability of code smells to explain maintenance problems: an empirical study combining quantitative and qualitative data

Code smells are indicators of deeper design problems that may cause difficulties in the evolution of a software system. This paper investigates the capability of twelve code smells to reflect actual maintenance problems. Four medium-sized systems with equivalent functionality but dissimilar design were examined for code smells. Three change requests were implemented on the systems by six software developers, each of them working for up to four weeks. During that period, we recorded problems faced by developers and the associated Java files on a daily basis. We developed a binary logistic regression model, with “problematic file” as the dependent variable. Twelve code smells, file size, and churn constituted the independent variables. We found that violation of the Interface Segregation Principle (a.k.a. ISP violation) displayed the strongest connection with maintenance problems. Analysis of the nature of the problems, as reported by the developers in daily interviews and think-aloud sessions, strengthened our view about the relevance of this code smell. We observed, for example, that severe instances of problems relating to change propagation were associated with ISP violation. Based on our results, we recommend that code with ISP violation should be considered potentially problematic and be prioritized for refactoring.     

基于排序损失的ECC多标签代码异味检测方法

代码异味是由糟糕的代码或设计问题引起的一种软件特征,严重影响了软件系统的可靠性和可维护性.在软件系统中,一段代码元素可能同时受到多种代码异味的影响,使得软件质量明显下降.多标签分类适用该情况,将高共现的多个代码异味置于同一标签组,可以更好地考虑代码异味的相关性,但现有的多标签代码异味检测方法未考虑同一段代码元素中多种代码异味检测顺序的影响.对此,提出了一种基于排序损失的集成分类器链(ensemble of classifier chains,ECC)多标签代码异味检测方法,该方法选择随机森林作为基础分类器并采取多次迭代ECC的方式,以排序损失最小化为目标,选择一个较优的标签序列集,优化代码异味检测顺序问题,模拟其生成机理,检测一段代码元素是否同时存在长方法长参数列表、复杂类消息链或消息链过大类这3组代码异味.实验采用9个评价指标,结果表明所提出的检测方法优于现有的多标签代码异味检测方法,F1平均值达97.16%.     

代码坏味研究综述

代码坏味(code smells)是低质量的急需重构的代码片段.代码坏味是软件工程领域的一个研究热点,并且相关研究方向众多、时间跨度大、研究成果丰富.为梳理相关研究思路和研究成果、分析研究热点并预判未来研究方向,对1990年至2020年6月间发表的代码坏味相关的339篇论文进行了系统地分析和归类,对代码坏味的发展趋势进行了分析与统计,量化揭示了相关研究的主流与热点.揭示了学术界关注的关键代码坏味,并研究了工业界与学术界的关注点的差异及其影响.     

Supporting requirements to code traceability through refactoring

In this paper, we hypothesize that the distorted traceability tracks of a software system can be systematically re-established through refactoring, a set of behavior-preserving transformations for keeping the system quality under control during evolution. To test our hypothesis, we conduct an experimental analysis using three requirements-to-code datasets from various application domains. Our objective is to assess the impact of various refactoring methods on the performance of automated tracing tools based on information retrieval. Results show that renaming inconsistently named code identifiers, using Rename Identifier refactoring, often leads to improvements in traceability. In contrast, removing code clones, using eXtract Method (XM) refactoring, is found to be detrimental. In addition, results show that moving misplaced code fragments, using Move Method refactoring, has no significant impact on trace link retrieval. We further evaluate Rename Identifier refactoring by comparing its performance with other strategies often used to overcome the vocabulary mismatch problem in software artifacts. In addition, we propose and evaluate various techniques to mitigate the negative impact of XM refactoring. An effective traceability sign analysis is also conducted to quantify the effect of these refactoring methods on the vocabulary structure of software systems.     

Identification of extract method refactoring opportunities for the decomposition of methods

The extraction of a code fragment into a separate method is one of the most widely performed refactoring activities, since it allows the decomposition of large and complex methods and can be used in combination with other code transformations for fixing a variety of design problems. Despite the significance of Extract Method refactoring towards code quality improvement, there is limited support for the identification of code fragments with distinct functionality that could be extracted into new methods. The goal of our approach is to automatically identify Extract Method refactoring opportunities which are related with the complete computation of a given variable (complete computation slice) and the statements affecting the state of a given object (object state slice). Moreover, a set of rules regarding the preservation of existing dependences is proposed that exclude refactoring opportunities corresponding to slices whose extraction could possibly cause a change in program behavior. The proposed approach has been evaluated regarding its ability to capture slices of code implementing a distinct functionality, its ability to resolve existing design flaws, its impact on the cohesion of the decomposed and extracted methods, and its ability to preserve program behavior. Moreover, precision and recall have been computed employing the refactoring opportunities found by independent evaluators in software that they developed as a golden set.     

A tool environment for quality assurance based on the Eclipse Modeling Framework

The paradigm of model-based software development has become more and more popular since it promises an increase in the efficiency and quality of software development. Following this paradigm, models become primary artifacts in the software development process. Therefore, software quality and quality assurance frequently leads back to the quality and quality assurance of the involved models. In our approach, we propose a model quality assurance process that can be adapted to project-specific and domain-specific needs. This process is based on static model analysis using model metrics and model smells. Based on the outcome of the model analysis, appropriate model refactoring steps can be performed. In this paper, we present a tool environment conveniently supporting the proposed model quality assurance process. In particular, the presented tools support metrics reporting, smell detection, and refactoring for models being based on the Eclipse Modeling Framework, a widely used open source technology in model-based software development.     

利用主轴因子法的严重性代码异味相关性分析

代码异味的存在对源代码的可理解性和可维护性有着糟糕的负面影响.通常情况下,研究人员更多是考虑单一代码异味对源代码的影响,但有研究指出,多种代码异味的共同存在以及它们之间的交互往往比单一代码异味有着更严重的负面影响.本文针对主成分分析在布尔类型变量分析中容易产生难以解释的主成分的弊端,提出了一种基于主轴因子法及异味严重性的代码异味相关性分析方法,并在92个系统上对14种代码异味进行试验,从中提取了6个因子,在相关矩阵中新发现了{Extensive Coupling、Long Parameter List}代码异味对的存在.最后本文比较分析了具有严重性标签的代码异味数据集的优势,解释了每个因子的含义并进行分类命名.     

To what extent can maintenance problems be predicted by code smell detection? – An empirical study

ContextCode smells are indicators of poor coding and design choices that can cause problems during software maintenance and evolution.ObjectiveThis study is aimed at a detailed investigation to which extent problems in maintenance projects can be predicted by the detection of currently known code smells.MethodA multiple case study was conducted, in which the problems faced by six developers working on four different Java systems were registered on a daily basis, for a period up to four weeks. Where applicable, the files associated to the problems were registered. Code smells were detected in the pre-maintenance version of the systems, using the tools Borland Together and InCode. In-depth examination of quantitative and qualitative data was conducted to determine if the observed problems could be explained by the detected smells.ResultsFrom the total set of problems, roughly 30% percent were related to files containing code smells. In addition, interaction effects were observed amongst code smells, and between code smells and other code characteristics, and these effects led to severe problems during maintenance. Code smell interactions were observed between collocated smells (i.e., in the same file), and between coupled smells (i.e., spread over multiple files that were coupled).ConclusionsThe role of code smells on the overall system maintainability is relatively minor, thus complementary approaches are needed to achieve more comprehensive assessments of maintainability. Moreover, to improve the explanatory power of code smells, interaction effects amongst collocated smells and coupled smells should be taken into account during analysis.     

A metamodeling approach for the identification of organizational smells in multi-agent systems: application to ASPECS

Software Quality is one of the most important subjects in the Process Development Software, especially in large and complex systems. Much effort has been devoted to the development of techniques and concepts to improve software quality over the years. We are especially interested on smells, which represent anomalies or flaws in the design/code that can have serious consequences in maintenance or future development of the systems. These techniques have a strong development in the Object Oriented paradigm, however, very few studies were conducted in the agent oriented paradigm. In this paper we focus on the detection of design smells applied to multi-agent systems models based on the organizational approach, named Organizational Design Smells (ODS). Early and automatic detection of these ODS allows reducing the costs and development times, while increasing the final product’s quality. To achieve this objective, validation rules were defined based in the EVL language. The approach is illustrated with two examples, their validation rules, and the refactoring solutions proposed.     

DECOR: A Method for the Specification and Detection of Code and Design Smells

Code and design smells are poor solutions to recurring implementation and design problems. They may hinder the evolution of a system by making it hard for software engineers to carry out changes. We propose three contributions to the research field related to code and design smells: 1) Decor, a method that embodies and defines all the steps necessary for the specification and detection of code and design smells, 2) Detex, a detection technique that instantiates this method, and 3) an empirical validation in terms of precision and recall of Detex. The originality of Detex stems from the ability for software engineers to specify smells at a high level of abstraction using a consistent vocabulary and domain-specific language for automatically generating detection algorithms. Using Detex, we specify four well-known design smells: the antipatterns Blob, Functional Decomposition, Spaghetti Code, and Swiss Army Knife, and their 15 underlying code smells, and we automatically generate their detection algorithms. We apply and validate the detection algorithms in terms of precision and recall on Xerces v2.7.0, and discuss the precision of these algorithms on 11 open-source systems.     

代码变更中抽取类重构模式的识别

在现代软件开发和维护中,重构是提高软件可维护性和软件质量的常用手段.而大量重构模式掺杂在日常的bug修复、功能增加等代码变更中,使得变更理解变得非常复杂.识别重构模式可以将重构与其它类型的代码变更隔离,利于变更理解.目前在识别重构模式的相关研究中,并没有结合变更类型和相似性比较的识别重构模式的方法及工具.为此,提出了一种基于细粒度变更类型和文本相似性比较识别重构模式的方法.将该方法应用于抽取类重构模式,并在4个开源项目中进行了实验,其平均准确率在82.6%左右.