package Foo;

sub new { bless {}, shift }

sub _method1 { print "Foo::_method\n"; }
sub method2 { my $self = shift; $self->_method1 }

package Foo::Bar;

@ISA = qw( Foo );

sub _method1 { print "Foo::Bar::_method\n"; }

package main;

my $foobar = Foo::Bar->new;
$foobar->method2;