Assessing the effect of source code characteristics on changeability

Maintenance is the phase of the software lifecycle that comprises any modification after the delivery of an application. Modifications during this phase include correcting faults, improving internal attributes, as well as adapting the application to different environments. As application knowledge and architectural integrity degrade over time, so does the facility with which changes to the application are introduced. Thus, eliminating source code that presents characteristics that hamper maintenance becomes necessary if the application is to evolve. We group these characteristics under the term Source Code Issues. Even though there is support for detecting Source Code Issues, the extent of their harmfulness for maintenance remains unknown. One of the most studied Source Code Issue is cloning. Clones are duplicated code, usually created as programmers copy, paste, and customize existing source code. However, there is no agreement on the harmfulness of clones. This thesis proposes and follows a novel methodology to assess the effect of clones on the changeability of methods. Changeability is the ease with which a source code entity is modified. It is assessed through metrics calculated from the history of changes of the methods. The impact of clones on the changeability of methods is measured by comparing the metrics of methods that contain clones to those that do not. Source code characteristics are then tested to establish whether they are endemic of methods whose changeability decay increase when cloned. In addition to findings on the harmfulness of cloning, this thesis contributes a methodology that can be applied to assess the harmfulness of other Source Code Issues. The contributions of this thesis are twofold. First, the findings answer the question about the harmfulness of clones on changeability by showing that cloned methods are more likely to change, and that some cloned methods have significantly higher changeability decay when cloned. Furthermore, it offers a characterization of such harmful clones. Second, the methodology provides a guide to analyze the effect of Source Code Characteristics in changeability; and therefore, can be adapted for other Source Code Issues

Tracking clones' imprint

Cloning imprint is the lasting effect of cloning on applications. This paper aims to analyze the clone imprint over time, in terms of the extension of cloning, the persistence of clones in methods, and the stability of cloned methods. Such level of detail requires an improvement in the clone tracking algorithms previously proposed, which is also presented. We found that cloned methods are cloned most of their lifetime, cloned methods have a higher density of changes, and that changes in cloned methods tend to be customizations to the clone environment

Assessing the effect of clones on changeability

To prioritize software maintenance activities, it is important to identify which programming flaws impact most on an application's evolution. Recent empirical studies on such a flaw, code clones, have focused on one of the arguments to consider clones harmful, namely, that related clones are not updated consistently. We believe that a wider notion is needed to assess the effect of cloning on evolution. This paper compares measures of the maintenance effort on methods with clones against those without. Statistical and graphical analysis suggests that having a clone may increase the maintenance effort of changing a method. The effort seems to increase depending on the percentage of the system affected whenever the methods that share the clone are modified. We also found that some methods seem to increase significantly their maintenance effort when a clone was present. However, the characteristics analyzed in these methods did not reveal any systematic relation between cloning and such maintenance effort increase

Understanding the Evolution of Code Clones in Software Systems

Code cloning is a common practice in software development. However, code cloning has both positive aspects such as accelerating the development process and negative aspects such as causing code bloat. After a decade of active research, it is clear that removing all of the clones from a software system is not desirable. Therefore, it is better to manage clones than to remove them. A software system can have thousands of clones in it, which may serve multiple purposes. However, some of the clones may cause unwanted management difficulties and clones like these should be refactored. Failure to manage clones may cause inconsistencies in the code, which is prone to error. Managing thousands of clones manually would be a difficult task. A clone management system can help manage clones and find patterns of how clones evolve during the evolution of a software system. In this research, we propose a framework for constructing and visualizing clone genealogies with change patterns (e.g., inconsistent changes), bug information, developer information and several other important metrics in a software system. Based on the framework we design and build an interactive prototype for a multi-touch surface (e.g., an iPad). The prototype uses a variety of techniques to support understanding clone genealogies, including: identifying and providing a compact overview of the clone genealogies along with their key characteristics; providing interactive navigation of genealogies, cloned source code and the differences between clone fragments; providing the ability to filter and organize genealogies based on their properties; providing a feature for annotating clone fragments with comments to aid future review; and providing the ability to contact developers from within the system to find out more information about specific clones. To investigate the suitability of the framework and prototype for investigating and managing cloned code, we elicit feedback from practicing researchers and developers, and we conduct two empirical studies: a detailed investigation into the evolution of function clones and a detailed investigation into how clones contribute to bugs. In both empirical studies we are able to use the prototype to quickly investigate the cloned source code to gain insights into clone use. We believe that the clone management system and the findings will play an important role in future studies and in managing code clones in software systems

Aspect of Code Cloning Towards Software Bug and Imminent Maintenance: A Perspective on Open-source and Industrial Mobile Applications

As a part of the digital era of microtechnology, mobile application (app) development is evolving with lightning speed to enrich our lives and bring new challenges and risks. In particular, software bugs and failures cost trillions of dollars every year, including fatalities such as a software bug in a self-driving car that resulted in a pedestrian fatality in March 2018 and the recent Boeing-737 Max tragedies that resulted in hundreds of deaths. Software clones (duplicated fragments of code) are also found to be one of the crucial factors for having bugs or failures in software systems. There have been many significant studies on software clones and their relationships to software bugs for desktop-based applications. Unfortunately, while mobile apps have become an integral part of today’s era, there is a marked lack of such studies for mobile apps. In order to explore this important aspect, in this thesis, first, we studied the characteristics of software bugs in the context of mobile apps, which might not be prevalent for desktop-based apps such as energy-related (battery drain while using apps) and compatibility-related (different behaviors of same app in different devices) bugs/issues. Using Support Vector Machine (SVM), we classified about 3K mobile app bug reports of different open-source development sites into four categories: crash, energy, functionality and security bug. We then manually examined a subset of those bugs and found that over 50% of the bug-fixing code-changes occurred in clone code. There have been a number of studies with desktop-based software systems that clearly show the harmful impacts of code clones and their relationships to software bugs. Given that there is a marked lack of such studies for mobile apps, in our second study, we examined 11 open-source and industrial mobile apps written in two different languages (Java and Swift) and noticed that clone code is more bug-prone than non-clone code and that industrial mobile apps have a higher code clone ratio than open-source mobile apps. Furthermore, we correlated our study outcomes with those of existing desktop based studies and surveyed 23 mobile app developers to validate our findings. Along with validating our findings from the survey, we noticed that around 95% of the developers usually copy/paste (code cloning) code fragments from the popular Crowd-sourcing platform, Stack Overflow (SO) to their projects and that over 75% of such developers experience bugs after such activities (the code cloning from SO). Existing studies with desktop-based systems also showed that while SO is one of the most popular online platforms for code reuse (and code cloning), SO code fragments are usually toxic in terms of software maintenance perspective. Thus, in the third study of this thesis, we studied the consequences of code cloning from SO in different open source and industrial mobile apps. We observed that closed-source industrial apps even reused more SO code fragments than open-source mobile apps and that SO code fragments were more change-prone (such as bug) than non-SO code fragments. We also experienced that SO code fragments were related to more bugs in industrial projects than open-source ones. Our studies show how we could efficiently and effectively manage clone related software bugs for mobile apps by utilizing the positive sides of code cloning while overcoming (or at least minimizing) the negative consequences of clone fragments

Causes and consequences of variation in female mate choice and its relation to sexual conflict in Drosophila melanogaster

Female mate choice is a significant driving force of evolutionary change and can explain the evolution of exaggerated male traits and/or displays, and dimorphism between the sexes. Females are thought to choose mates based on the greatest provision of direct or indirect benefits. Despite this, we often still see substantial individual variation in female mate choice behaviours both within and across populations. Recent studies suggest that female mate choice is a complex decision-making process that involves many context-dependent factors. However, the precise sources of this variation, such as previous mating experience, are not completely understood. In Drosophila melanogaster, mating can be harmful and have costly effects on a female\u27s lifetime fitness. As such, sexual conflict theory predicts that females may make trade-offs in their mate choice decisions to balance the direct costs and indirect benefits associated with mating. In this thesis, I set out to understand if the harmfulness of a previous mating experience influences a female\u27s subsequent mate choice behaviours. In chapter two of this thesis, I assessed the effect of male exposure on female fitness by measuring the change in their fecundity (a meaningful metric of fitness) across a brief and prolonged period of exposure. In this experiment, we found that the degree that different males harm their mates across this time period largely depended on the male\u27s genetic background. Using these results, I was able to quantify the harmfulness of 26 male hemiclone lines that each possess a unique genetic background. In chapter three of this thesis, I used these quantified males to examine if the direct costs of a previous mating experience has an effect on subsequent female mate choice behaviours and to quantify the degree of additive genetic variation associated with this effect. The results of my studies suggest that females alter their mate choice behaviours based on previous mating experiences, and that the degree to which these behaviours change has a genetic basis. I discuss how these results are significant for our understanding of the evolution of female mate choice, and the maintenance of variation in harmful male traits