update: since the OP replaced his original question, the answer below doesn't make much sense.

There is an example snippet right at the top of the module's documentation:

         use Getopt::Long;
         my $data   = "file.dat";
         my $length = 24;
         my $verbose;
         $result = GetOptions ("length=i" => \$length,    # numeric
                               "file=s"   => \$data,      # string
                               "verbose"  => \$verbose);  # flag
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This will set the $length, $data and $verbose variables according to the --length (with integer value), --file (with string value) and --verbose (boolean switch) options passed to the script.

Getopt::Long does indeed have only one public function in its API, because you don't need more than one function. Your statement that every Java API has more than one method is wrong: here's one with only 1 method

A module is just perl code in a file that has a .pm extension. It doesn't even have to have any public methods/functions.

See perlmod and perlmodlib for much more info about using and creating modules.