thesis - Faculty of Information and Communication Technologies ...

Chapter 4. Measuring Evolving Software
sub-set of classes that they use from this package. Furthermore,
the type names within the source code typically contain just the
class name, not the fully qualified name (for example, it is more
common to use Math rather than java.lang.Math when the developers
rely on mathematical library functions).
• All comments are removed from compiled class files.
• The compilation process typically erases local variable names and
hence we lose these symbol names in the compiled class.
• A compiled class contains a constant pool which is an array containing
all the numeric, string and type constants that are used in
the class. These constants are defined only once in the constant
pool and referenced (via an index) in all other sections of the class.
Metrics Extraction and Post Processing
We process each compiled Java class file and extract two types of metrics:
direct count metrics and modifier flags. Table 4.2 shows the list of
count metrics that we extract by processing field and method interface
information for each class, Table 4.3 shows the list of count metrics
that are computed by processing the bytecode instructions present in
method bodies, and Table 4.4 shows the flags that we extract for each
class. In this thesis, we treat all the count metrics as measures of size
as they reflect size of a class from different perspectives. However, we
consider the Number of Branches (NOB) measure as a complexity metric
that captures the internal structure of a class. The NOB measure is
equivalent to the widely used Weighted Method Count (WMC) metric [46]
with Cyclomatic Complexity [190] used as the weight [46]. The WMC
and (hence our formulation of the NOB) is accepted within the literature
as a measure of structural complexity [116, 165].
Along with the metrics shown in Tables 4.2, 4.3, and 4.4 we also capture
the fully qualified name of each class, its fully-qualified super class
name as well as all method names (including full signature capturing
the return type), field names (including the type) and the fully-qualified
name of all other classes that a class depends upon.
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