Global symbol "$buffer" requires explicit package name at ...
Global symbol "@output" requires explicit package name at ...
Global symbol "%states" requires explicit package name at ...

##</code><code>##

my ($buffer, @output, %states);

##</code><code>##

our ($buffer, @output, %states);

##</code><code>##

package DFA;
sub new {
  my $dfa = {};
  bless $dfa, shift;   # associates $dfa with the current package
  $dfa->{buffer} = '';
  $dfa->{output} = []; # note: output is now an array reference
  $dfa->{states} = {}; # note: states is now a hash ref
  $dfa;                # return the new object
}
...

##</code><code>##

sub argout {
  my $dfa = shift;      # $dfa here is equivalent to 'this' in Java
  my $temp = { type => 'ARG', value => $dfa->{buffer} };
  $dfa->{buffer} = '';
  push(@{$dfa->{output}}, $temp);
}

# example of constructing a DFA object and calling argout:

my $dfa = DFA->new();
$dfa->argout();