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Chapter 4. Measuring Evolving Software
1 /∗∗ A simple method to print " Hello World" to console ∗/
2 public void printHelloWorld ( )
3 {
4
5 System . out . println ( " Hello World " ) ;
6
7 // Annotated bytecode instructions
8 // Numbers that start with a # are the index into the constant pool
9
10 // getstatic #5; //LOAD Field java/lang/System. out : java/io/PrintStream
11 // ldc #6; //LOAD String Hello World
12 // invokevirtual #7; //CALL Method java/io/PrintStream . println
13 // return
14 }
Listing 4.1:
method
Same of bytecode generated for a simple Hello World
by zero or more operands which contain the values to be operated
upon [180]. There are a total of 256 possible opcodes instructions that
can be generated by the compiler and all of these instructions are embedded
in the method body (see Table 4.1). We process the bytecode
instructions and determine the nature of the operation in order to compute
appropriate metrics. The sample code in Listing 4.1 for a “Hello
World” method shows the set of bytecode instructions that are generated
as comments within the method body. In this sample listing, there
are 4 bytecode instructions generated from a single line of source code
(three bytecode instructions take a single operand, while one of the operations
has zero operands). In our study, we process these bytecode
instructions, as well as all of the other information embedded in the
compiled class (as indicated in Table 4.1) to compute the various metrics.
A fully annotated Java program is presented in Appendix D to
further illustrate how our metric extraction approach counts the various
metrics from the compiled class file.
Differences between source code and compiled code
Though, the compiled Java class is close to the source code, there are
some differences:
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