Re: Line numbers in stack trace

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 13 Mar 2009 23:54:03 -0400

Message-ID:

<gpf9ot$mp$1@news.albasani.net>

Manish wrote ...

One thing that has always interested me is that whenever the stack
trace is printed when an exception occurs, the line number(s) of the
line(s) which caused the exception are also printed.

....

Is there any article/post which explains how such a feature is
implemented in java [sic]? If this question has already been answered could
someone please direct me to the correct page ?

Arved Sandstrom wrote:

The JVM spec will give you this info. After all, the line number information
(if you see it - you may not if the JIT compiler has already kicked in) will
be in the class file if at all. For example:

http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html#22856

There is also the Java tools documentation, which for javac tells us of the
'-g' option:

-g:{keyword list}
    Generate only some kinds of debugging information,
specified by a comma separated list of keywords.
Valid keywords are:
    source
        Source file debugging information
    lines
        Line number debugging information
    vars
        Local variable debugging information

From this we see that such information is put in the class file somehow, to
the how of which Arved has already pointed us.

As for JIT/Hotspot, I suspect that an exception might cause the JVM to look at
the bytecode before reporting the problem, thus recovering any debug
information even after optimization. Also, IIRC, '-g' suppresses certain
optimizations, though I might be wrong about that.

--
Lew