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};
}

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 $self->{_firstName};
}

# Add more methods
sub setLastName{
my ( $self, $lastName ) = @_;
$self->{_lastName} = $lastName if defined($lastName);
return $self->{_lastName};
}

sub getLastName {
my( $self ) = @_;
return $self->{_lastName};
}

use Employee;

$object = new Employee( "Mohammad", "Saleem", 23234345);
# Get first name which is set using constructor.
$firstName = $object->getFirstName();

print "Before Setting First Name is : $firstName\n";

# Now Set first name using helper function.
$object->setFirstName( "Mohd." );

# Now get first name set by helper function.
$firstName = $object->getFirstName();
print "After Setting First Name is : $firstName\n";