Mostly Harmless

When debugging my Java programs, reading through the exception stack trace I realized that many a times the line number in was not reported. Just the method name and file name with unknown source was reported. For example consider the following simple program compiled with build file as shown

//File: TestDebug.java
public class TestDebug {
    public static void main(String[] args) {
        ((String)null).length();
    }
}

<!-- build.xml -->
<project name="TestProject" default="build" basedir=".">
 <target name="build">
  <javac srcdir="." destdir="."/>
 </target>
</project>

[nilesh^trinity]$ ant build
...
[nilesh^trinity]$ java TestDebug
Exception in thread "main" java.lang.NullPointerException
        at TestDebug.main(Unknown Source)

After some investigation I found that ant omits debug information from compiled class by default. Hence producing exact line number in case of an error is not possible. The solution however is simple. I just modified my build file to turn debug on and to set debuglevel="lines,vars,source" under javac target in ant, and everything worked fine. Modified build file for above example will be:

<!-- build.xml -->
<project name="TestProject" default="build" basedir=".">
 <target name="build">
  <javac srcdir="." destdir="." debug="on" debuglevel="lines,vars,source" />
 </target>
</project>

Line numbers are now reported with the stack trace:

[nilesh^trinity]$ ant build
...
[nilesh^trinity]$ java TestDebug
Exception in thread "main" java.lang.NullPointerException
        at TestDebug.main(TestDebug.java:4)

# posted by nileshbansal @ 1:54 am - -   -bookmark at -del.icio.us   -