<?php

abstract class Foo {

    private $e;

    public function setE($val) {
       $this->e = $val;
    }

    public function getE() {
       return $this->e;
    }

}

class Bar extends Foo {
    
}

$bar = new Bar;
$bar->setE('hello');
var_dump( $bar->getE() );

string(5) "hello"