CS201, Mock
Debugging
Some have said that any monkey can write a program – the hard part is debugging it.
While this is somewhat oversimplifying the difficult process of writing a program, it is
sometimes more time consuming and frustrating to debug a program than it was to write
it in the first place. However there are tools to help you! The purpose of this lecture is to
introduce you to some of these tools.
In this lecture we’ll look at two methods of debugging:
1. Adding print statements, which has the benefit of working in any programming
language and in any environment, but is very tedious and can sometimes actually
lead to errors
2. Using the debugging utilities in NetBeans (similar tools exist in most IDE’s)
There is also a debugger in Unix called jdb for the Java environment. We won’t cover it
here, but you should be aware that it exists if you plan to do more development under
Unix.
Debugging with Print Statements
You have probably already used this method for debugging. The basic idea is very
simple. If your program is not working correctly, try inserting print statements (in Java,
this would be System.out.println statements) to narrow down where the error is. The
print statements could be used to locate the section of code that contains the problem, and
they might output the values of some variables that would aid in debugging.
As one example, consider the program below:
class DebugTest {
public static final String STR = "some string here";
public static void main(String[] args) {
String s;
s = STR.substring(0,3);
// Do some processing of the string
s = STR.substring(1,5);
// Do some processing of the string
s = STR.substring(8,3);
// Do some processing of the string
s = STR.substring(22,4);
// Do some processing of the string
s = STR.substring(2,3);
// Do some processing of the string
return;
}
}
