thesis - Faculty of Information and Communication Technologies ...
thesis - Faculty of Information and Communication Technologies ...
thesis - Faculty of Information and Communication Technologies ...
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Chapter 5. Growth Dynamics<br />
Another dimension <strong>of</strong> machine generated code was observed when we<br />
investigated two systems PMD <strong>and</strong> Checkstyle that had very high Gini<br />
Coefficient values for Number <strong>of</strong> Attributes <strong>and</strong> Number <strong>of</strong> Methods. Interestingly<br />
these systems had a substantial number <strong>of</strong> classes with either<br />
zero fields or zero methods. This zero inflation increases the Gini<br />
Coefficient value. But, what type <strong>of</strong> design choices cause such an unusual<br />
shape? Interestingly, both PMD <strong>and</strong> Checkstyle serve a similar<br />
purpose. These tools help developers check that Java source code adheres<br />
to specified coding conventions <strong>and</strong> st<strong>and</strong>ards. This functionality<br />
is provided via a set <strong>of</strong> configurable rules around coding st<strong>and</strong>ards, formatting<br />
rules <strong>and</strong> source code metrics.<br />
A deeper investigation showed that both Checkstyle <strong>and</strong> PMD represent<br />
the Java source code that they process by constructing an Abstract Syntax<br />
Tree (AST) <strong>and</strong> use the visitor pattern to walk the nodes in the tree.<br />
In both these systems, the rules to check source code were developed<br />
by extending an abstract rule class with the child class providing the<br />
rule implementation. The rules that developers could configure <strong>and</strong><br />
add in these tools were written without making use <strong>of</strong> any fields <strong>and</strong><br />
<strong>of</strong>ten encapsulated within a single method to satisfy the visitor pattern.<br />
This design approach created a large number <strong>of</strong> “poor" classes making<br />
those that actually possessed more functionality look unusually rich,<br />
pushing the Gini coefficient value closer to 1.<br />
5.6 Summary<br />
Evolving s<strong>of</strong>tware tends to exhibit growth. In this chapter our focus was<br />
on how maintenance effort is distributed by analyzing class size <strong>and</strong><br />
complexity metric distributions. The data we collected for our study<br />
showed that size <strong>and</strong> complexity are unevenly distributed, confirming<br />
similar observations made by other researchers. However, these skewed<br />
distributions cause st<strong>and</strong>ard statistical summary measures such as<br />
mean <strong>and</strong> st<strong>and</strong>ard deviation to provide misleading information making<br />
their application for comparative analysis challenging. In order to<br />
overcome this limitation, we analyzed the data using Gini coefficient, a<br />
higher-order statistic widely used in economics to study the distribution<br />
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