package Person;

sub new
{
    my $class = shift;
    my $self = {
        _firstName => shift,
        _lastName  => shift,
        _ssn       => shift,
    };
    # Print all the values just for clarification.
    print "First Name is $self->{_firstName}\n";
    print "Last Name is $self->{_lastName}\n";
    print "SSN is $self->{_ssn}\n";
    bless $self, $class;
    return $self;
}
sub setFirstName {
    my ( $self, $firstName ) = @_;
    $self->{_firstName} = $firstName if defined($firstName);
    return $self->{_firstName};
}


sub getFirstName {
    my( $self ) = @_;
    return $self->{_firstName};
}
1;

***************************************************




package Employee;
use Person;
use strict;
our @ISA = qw(Person);    # inherits from Person


# Override constructor
sub new {
    my ($class) = @_;

    # Call the constructor of the parent class, Person.
    my $self = $class->SUPER::new( $_[1], $_[2], $_[3] );
    # Add few more attributes
    $self->{_id}   = undef;
    $self->{_title} = undef;
    bless $self, $class;
    return $self;
}

# Override helper function
sub getFirstName {
    my( $self ) = @_;
    # This is child class function.
    print "This is child class helper function\n";
    return 0;
}