<?php
class foo
{
    public function init()
    {
        $this->doSomething(); 
    }

    function doSomething()
    {
        //intentionaly no functionality here
    }


}

class bar extends foo
{
    function doSomething()
    {
        echo get_class( $this) . " says: baz \n";
    }
}

class baz extends foo
{
    function doSomething()
    {
        echo get_class( $this) . " says: hello \n";
    }
}

$barInstance = new bar();
$bazInstance = new baz();
$barInstance->init();
$bazInstance->init();

bar says: baz 
baz says: hello