Assuming you are looking for all comments in some nasty(large) java programs, first what are all the possible ways a comment can be mal-formed? And are they critical to your life goal?

That said here is a sample input file with a few interesting possibilities (yes it compiles):

/**
 *  The HelloWorldApp Class impliments an application that displays "H
+ello World!" to standard output
 */
public class HelloWorldApp
 {
    public static void main (String[] args)
    {
       // Display "Hello World!"
       System.out.println("Hello World!"); // end of line comment
       System.out.println("Hello World!"); /* end of line comment */
       System.out.println("Hello World!/*"); /* end of line comment */
/* this
is
a
multi
line
comment
*/
/* another comment */
// /* is this a valid comment
/*
//  */
       System.out.println("//Hello World!/*"); // is /* this valid
    }
 }
[download]

Below is some rough code to start grabbing comments. Coding for the cute exceptions is left as an exercise for the student (I hava always wanted to use that line, since it was used on me a long time ago) or as future discussion points. It prints the line number of the file where the comment begins and then the comment.

#!/usr/bin/perl
use strict;
my $infile = "HelloWorldApp.java";
my %linehash;
my $linecounter =0;
my $comment_started = 0;
my $multiline_comment;
open in, "$infile" or die "could not open $infile\n";
while (<in>)
{
## you may need to get creative in matching comments
## because java allows some fun combinations - see HelloWorld
##
## grab single line comments first else look for multiline
  if (/\/\/.*\n/ || /\/\*.*\*\//)
  {
     $linehash{$linecounter} = $_;
  }
  else
  {
## possible multiline comment start
    if ($comment_started)
    {
      $multiline_comment = $multiline_comment . $_;
## don't mess with $_ as later comparisons may need the newline in pla
+ce
      chomp $multiline_comment;
      $multiline_comment = $multiline_comment . " ";
##  end of multiline comment
      if (/\*\//)
      {
        $linehash{$comment_started} = $multiline_comment;
        $comment_started = 0;
        $multiline_comment = "";
      }
    }
## start multiline comment
    if (/\/\*/)
    {
      $comment_started=$linecounter;
    }
  }
  $linecounter++;
}
my @keys = sort{$a <=> $b}(keys(%linehash));
for (@keys)
{
  print "key=$_   value=$linehash{$_}";
}
[download]

Enjoy
John